Retractor systems with sensors

ABSTRACT

A retractor system includes a retractor with an oximeter sensor at its tip and a force sensor coupled to the retractor. The retractor system also includes a system unit which can send signals to and receive signals from the oximeter sensor via optical fibers. The oximeter sensor measures oxygen saturation of a tissue being retracted by the retractor, and the force sensor measures an amount of force that is applied to the retracted tissue by the tip of the retractor. Another retractor system has a closed loop control arrangement with a positioning mechanism which moves the retractor based on measurements of the sensors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 15/346,692, filed Nov. 8, 2016, issued as U.S. Pat. No.10,835,227 on Nov. 17, 2020, which is a divisional of U.S. patentapplication Ser. No. 12/365,735, filed Feb. 4, 2009, issued as U.S. Pat.No. 9,486,196 on Nov. 8, 2016. These applications are incorporated byreference along with all other references cited in this application.

BACKGROUND OF THE INVENTION

This invention relates to the field of medical devices and morespecifically to a tissue retractor with a sensor.

Retractors play an important role in medicine. Retractors retract orhold aside tissue (e.g., nerve root, spinal cord, facial nerve, muscle,liver, kidney, and others) so that a surgeon can gain access to an areafor operation or observation. There are a variety of retractors fordifferent tissue types. All retractors physically contact a tissue andtypically apply a certain amount of pressure to the tissue at the pointof contact during retraction.

It is important that retracted tissues are not damaged duringretraction. With current retractors, however, it is difficult, if notimpossible, to tell whether the tissues are being damaged during theretraction. Damage to any tissue can be devastating, which can result indiminished or loss of its function or pain. For example, damage to nerveroot or any nerve is undesirable, leading to loss of sensation,numbness, or pain to the patient.

There is, then, a continuing demand for retractors and other medicaldevices that can perform their function without damaging retractedtissues. It would also be desirable to develop retractors and medicaldevices that provide patient feedback, provide more features, are easierto use, and generally address the needs of patients, doctors, and othersin the medical community.

Therefore, there is a need to provide improved systems and techniquesfor retractors.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the invention, a retractor system has a retractorincluding a shaft having a proximal end and a distal end, a tipconnected to the distal end of the shaft, where the tip has a retractorportion and an oximeter sensor. The retractor system also includes aforce sensor connected to, in, contained within, or part of theretractor. The retractor system further includes a system unit that hasa display, processor, signal emitter circuit, and signal detectorcircuit. The retractor system can further include a receptacle forconnecting optical fibers.

In one implementation of the system, the retractor system has anoximeter sensor including a first sensor opening and a second sensoropening on a bottom side of the tip. The retractor system also has afirst optical fiber and a second optical fiber. The first optical fiberpasses through a channel in the shaft and a distal end of the firstoptical fiber is connected to a first sensor opening of the tip. Thesecond optical fiber passes through the channel in the shaft and adistal end of the second optical fiber is connected to a second sensoropening of the tip.

In another implementation of the system, the retractor system has asingle optical fiber or single optical fiber bundle, where its distalend is connected to a single sensor opening on a bottom side of the tip.In an embodiment where a single optical fiber bundle is used, opticalfibers in the bundle are split into two separate bundles at theirproximal end so that some of the optical fibers are connected to a lightsource and the rest of the optical fibers in the bundle are connected toa detector. In another embodiment where a single optical fiber is used,a fiber combiner is used to combine a proximal end of the single opticalfiber with two separate optical fibers—one optical fiber connecting thesingle optical fiber to a light source and the other optical fiberconnecting the single optical fiber to a detector.

In another aspect of the invention, the retractor system for retractinga tissue has a closed loop control system. The retractor system includesa retractor having a sensor. The retractor system also includes apositioning mechanism which is connected to the retractor. The retractorsystem further includes a controller which is connected to the sensorand the positioning mechanism. The sensor measures some parameter thatreflects the health or condition of a retracted tissue, and theparameter is transmitted as an input signal to the controller. Thecontroller generates a control signal to control movement of thepositioning mechanism based on the input signal from the sensor. Theretractor in turn moves according to movement of the positioningmechanism.

The control signal from the controller actuates the retractor, throughmovement of the positioning mechanism, if the input signal from thesensor does not meet a threshold level or is not within a desired range.In other words, a retraction force applied to the retractor and aretraction distance of a tissue are adjusted based on the input signalfrom the sensor. The system can continuously monitor the parametermeasured by the sensor and can adjust a retraction force applied to theretractor so that the parameter of the retracted tissue can bemaintained above a threshold level or within a desired range.

In one embodiment, the retractor system includes a retractor having anoximeter sensor. The oximeter sensor measures oxygen saturation level ofa retracted tissue. During surgery, it is desired that oxygen saturationlevel of a retracted tissue remains above a certain level so that theretracted tissue does not suffer hypoxia. The oximeter sensor cancontinuously monitor oxygen saturation level of the retracted tissue,and this information can be transmitted to the controller. Thecontroller compares the measured oxygen saturation to a desired oxygensaturation level for the tissue. The system can then make an appropriateadjustment to a retraction force applied to the retractor so that theoxygen saturation level of the retracted tissue returns to above thecertain level or within a desired range.

In another embodiment, the retractor system includes a nerve retractorhaving a sensor. A nerve retractor has a sensor at its tip, which isused to contact and pull aside a nerve. The sensor can measure variousparameters of a retracted nerve, including an oxygen saturation level,temperature, color, and others. In one implementation of the invention,the sensor has at least one source structure including a fiber opticcable and at least one detector structure including a fiber optic cable.

In another embodiment, the retractor system further includes a forcesensor which is connected to a retractor and a positioning mechanism.The force sensor measures a force applied to a tissue by a tip of theretractor when the positioning mechanism alters a position of theretractor. The force applied to the tissue can be continuously monitoredand can be used as another input signal for the controller to determinea control signal for controlling movement of the positioning mechanism.

In another embodiment, a method includes determining a parameter of atissue that is retracted by a retractor using a sensor which isconnected to the retractor, determining if the parameter is above afirst value, and producing a control signal to alter a position of theretractor if the parameter is not above a first value. In someembodiments, the method further includes determining if the parameter isbelow a second value, where the second value is greater than the firstvalue, and producing a control signal to alter a position of theretractor if the parameter is not below the second value. These methodsteps can be continuously repeated to maintain the parameter of aretracted tissue above the first value or between the first value andthe second value.

Embodiments of the invention can be applied to retract any tissue. Inone implementation, the retractor system includes a nerve retractor toretract a nerve tissue, such as a spinal cord, nerve root, facial nerve,peripheral nerve and others. In another implementation, the retractorsystem includes an organ retractor of varying shape and size to retracta liver, kidney, lung, brain, muscle, stomach, intestine, uterus, ovary,bladder, bone, prostate, thyroid, parathyroid, adrenal gland, pancreas,spleen, heart, and others.

Other objects, features, and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionand the accompanying drawings, in which like reference designationsrepresent like features throughout the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a retractor system including a closedloop control system. The system has a retractor for retracting a tissue,where the retractor includes sensor for measuring a parameter of thetissue so that the parameter of the tissue can be maintained above athreshold level or within a desirable range.

FIG. 2A shows a specific implementation of the system of FIG. 1 .

FIG. 2B shows a flow diagram for a method of using a retraction systemto measure an oxygen saturation value of a retracted tissue andmodifying a retraction force applied to a retractor according to themeasured oxygen saturation value of the retracted tissue.

FIG. 3A shows a side view of a retractor device and a direction of forceapplied.

FIG. 3B shows a top view of the retractor device shown in FIG. 3A.

FIG. 3C shows details of a retractor device having an oximeter sensor atits tip and a force sensor near a handle.

FIG. 3D shows a photograph of mechanics of a retractor system.

FIG. 4 shows a block diagram of a retractor system that can be usedwithout a closed loop control arrangement.

FIG. 5 shows a side view of a retractor having an oximeter sensor at itstip.

FIG. 6 shows a side view of a tip connected to the shaft of a retractor.

FIG. 7 shows a bottom view of a tip with a single light source andsingle detector symmetrical array.

FIG. 8 shows a bottom view of a tip with a two light source and twodetector symmetrical array.

FIG. 9 shows a bottom view of a tip with a two light source and twodetector symmetrical array.

FIG. 10 shows a bottom view of a tip with a two light source and twodetector asymmetrical array.

FIG. 11 shows a geometric sensor arrangement with four sensors having aspacing relative to a y-axis.

FIG. 12 shows a geometric sensor arrangement with four sensors having aspacing relative to an x-axis.

FIG. 13 shows a geometric sensor arrangement with three sensors having aspacing relative to a y-axis.

FIG. 14 shows a geometric sensor arrangement with three sensors having aspacing relative to an x-axis.

FIG. 15 shows a geometric sensor arrangement with two sensors having aspacing relative to an x-axis.

FIG. 16 shows a sensor opening pattern where one sensor opening isaligned asymmetrically with respect to the other sensor openings.

FIG. 17 shows another sensor opening pattern where one sensor opening isaligned asymmetrically with respect to the other sensor openings.

FIG. 18 shows another sensor opening pattern where one sensor opening isaligned asymmetrically with respect to the other sensor openings.

FIG. 19A shows a sensor opening pattern where the openings are alignedin a row, except for one of the openings.

FIGS. 19B-1 and 19B-2 show a retractor oximeter that has a single sensoropening at the tip and a single optical fiber bundle connected to thesensor opening at a distal end.

FIGS. 19C-1, 19C-2, and 19C-3 show a retractor oximeter that has asingle sensor opening at the tip and a distal end of a single opticalfiber connected to the sensor opening, and a proximal end of the singleoptical fiber combined with two optical fibers by a fiber combiner.

FIG. 20 shows a retractor system including a system unit and a sensorprobe.

FIG. 21 shows detail of a specific implementation of the system of FIG.20 .

DETAILED DESCRIPTION OF THE INVENTION

During surgery a tissue that needs to be operated on is sometimes buriedunderneath or concealed by another tissue in a body. In such acircumstance, tissue retractors can be used to expose the surgical site.However, when the retractors are handled and adjusted by hand, it isdifficult for the surgeon to determine how much force the retractors areapplying on the tissue. For example, when a retractor is pulling anerve, it may be compressing the nerve with too much force at the pointof contact or it may be crushing a blood vessel (e.g., blood vesselsbundled with the nerve) or other vital surrounding tissues.

The surgical retraction can result in a structural damage to the tissueor tissue ischemia due to lack of blood flow. Tissue ischemia caused byretraction or local trauma can be particularly devastating if thedamaged tissue involves a nervous system. The additive force of surgicalretraction may further damage a nerve tissue that has already beencompromised. An abrupt decrease in blood flow to a nerve tissue canresult in permanent sensory or motor deficit or both. For example, bydepriving sufficient blood flood through the nerve caused by theretraction, the nerve may be deprived of oxygen. With insufficientoxygen, the nerve may die or be partially damaged. The amount of timethe nerve has been retracted may also be a factor in whether it will bedamaged.

The retractor system in accordance with the present invention allows thesurgeon to monitor the condition of a retracted tissue in real time,while retracting the tissue. Typically, one or more parameters thatreflect the condition of a retracted tissue are measured duringretraction. If the measured parameters indicate that the condition ofthe retracted tissue is deteriorating, a corrective measure can be takenimmediately during surgery to improve the condition of the retractedtissue. Accordingly, any potential damage to the retracted tissue can beminimized.

In embodiments of the invention, a retractor system includes a retractorhaving one or more sensors, which are connected to, in, containedwithin, or part of the retractor. The sensors can measure parameters ofthe tissue while being retracted. Based on the measured parameters, theretractor system can adjust a retraction force applied to a tip of theretractor so that certain parameters of the tissues can be maintainedabove a threshold level or within a desired range. For example, theparameters that can be measured by the sensors include oxygen saturationlevel of the retracted tissue, tissue temperature, tissue color, andothers.

In one implementation, a retractor includes an oximeter sensor. When atissue being retracted is compressed with too much force, then bloodflow to the retracted tissue will diminish and the tissue oxygensaturation level may decrease. The oximeter sensor can measure oxygensaturation level of the retracted tissue, and this information can betransmitted to a controller in the system so that a retraction forceapplied to the retractor tip can be adjusted. The oxygen saturationlevel or other measurable parameters can be continuously monitoredduring retraction so that stress on the retracted tissue can beminimized.

In another implementation, a retractor device or system includes a forcesensor and an oximeter sensor, and can be used without closed loopcontrol arrangement. Thus, the retractor device and system cansimultaneously measure two parameters of a retracted tissue-oxygensaturation level of the retracted tissue contacting the tip of theretractor device and an amount of force applied to the retracted tissueby the tip. By having both oximeter sensor and force sensor, theretractor device can better assist determining the effect of surgicalmanipulation on the health of nerve roots and other tissues.

Embodiments of the present invention provide several advantages. Byproviding various feedback signals measured from one or more sensors tothe controller, the oxygen saturation level or other measurableparameters of a retracted tissue can be maintained above a thresholdlevel or within a desired range without large fluctuations duringsurgery. A retraction distance and retraction force can also beautomatically and continuously adjusted, as necessary or desired, duringa surgical procedure. Since corrective measures are taken immediatelyduring surgery, any damage to a retracted tissue can be minimized.Furthermore, in some embodiments, since movement of the retractor systemis controlled mechanically, it eliminates a concern over the surgeon'shand tremor negatively impacting the surgery.

Aspects of the invention can be embodied in retractors of any type andfor any purpose. For example, these include retractors for a spinalcord, nerve root, peripheral nerve, facial nerve, brain, muscle,connective tissue, liver, kidney, uterus, ovary, stomach, intestine,bladder, bone, prostate, thyroid, parathyroid, adrenal gland, pancreas,spleen, heart, and others, and combinations of these. These retractorsretract tissue, organs, and other parts of the body (or body parts). Forthis application, “tissue” and “organ” are used interchangeably to referto any body part or aggregate of cells. In other words, “tissue” may beused to refer to an organ, and vice versa.

Examples of embodiments of the invention are illustrated using figuresand are described below. The figures described herein are used toillustrate embodiments of the invention, and are not in any way intendedto be restrictive of the broad invention. Embodiments of the inventionare not limited to the specific arrangements and constructions shown anddescribed. For example, features shown in one figure can be combinedwith other features shown in another figure.

FIG. 1 illustrates a block diagram of a system 100 that has a closedloop control arrangement. System 100 includes a retractor 110 which isused to retract a tissue. Retractor 110 includes a sensor 120. System100 also includes a positioning mechanism 130 which is connected toretractor 110. The positioning mechanism adjusts a position of theretractor so that a tip of the retractor can retract or hold aside atissue to a desired location, allowing the surgeon to gain access thesurgical site. When the tissue is pulled or retracted by the retractorthrough movement of the positioning mechanism, a certain amount of forceis applied to a tip of the retractor (and also on the tissue). Thisforce is referred to as “retraction force.”

System 100 also includes a controller 150. Controller 150 receives aninput signal from sensor or transducer 120 which measures a parameterassociated with the retracted tissue. Based on the input signal from thesensor, the controller produces a control signal which controls movementof positioning mechanism 130. In turn, the positioning mechanism adjustsa position of the retractor. The system can continuously monitor theparameter measured by the sensor and adjust a retraction force appliedto the retractor so that the parameter of the retracted tissue can bemaintained above a first threshold level, below a second threshold level(different from the first), or within a desired range.

In one embodiment of the invention, sensor 120 is an oximeter sensor,which is connected to, in, contained within, or part of retractor 110.The oximeter sensor measures an oxygen saturation value of a retractedtissue. This information is transmitted to controller 150. Thecontroller compares the measured oxygen saturation value of theretracted tissue to a predetermined oxygen saturation level or rangethat the user desires to maintain during retraction.

For example, during surgery a tissue may be retracted to a givendistance by a retractor to expose a surgical site, and the surgeon maydesire to maintain an oxygen saturation value of the retracted tissuebetween about 30 and 45 percent to avoid hypoxia and damage to thetissue. During surgery, if the measured oxygen saturation of theretracted tissue is within 30 to 45 percent, then the retractor may holdaside the tissue at the given distance with a constant retraction force.However, if the measured oxygen saturation of the retracted tissue goesbelow or above the predetermined 30 to 45 percent range, then theretraction force applied to a tip of the retractor can be adjusted sothat the oxygen saturation value of the retracted tissue returns back tothe predetermined 30 to 45 percent range.

During surgery, a desire for maintaining a relatively healthy oxygensaturation level for a retracted tissue is balanced against a need toretract the tissue to a distance that is desired (may be referred to asan “initially selected distance”) to expose the surgical site.Typically, the tissue is initially retracted to an initially selecteddistance by a retractor, and the oxygen saturation level of theretracted tissue is monitored. If the oxygen saturation level of theretracted tissue falls below a threshold level, then the controllerreduces a retraction distance to minimize stress on the retractedtissue. When the oxygen saturation level of the retracted tissuestabilizes and returns back to the threshold level, then the controllerincreases the retraction distance towards the initially selecteddistance so that the surgeon can readily access the surgical site.

In another embodiment, system 100 may include a different sensor inaddition or in alternative to the oximeter sensor. For example, a forcesensor can be included in the system. A force sensor is connected toboth the retractor and the positioning mechanism so that the forcesensor measures an amount of force that is applied to a tissue at theretractor tip by movement of the positioning mechanism. The amount offorce that is applied to the retractor tip can be continuously monitoredand can be used as another input signal for the controller to determinea control signal for controlling the positioning mechanism.

For instance, it may be determined from previous trials that when acertain amount of force is applied to a particular tissue duringretraction, it can either break or damage the tissue. Then it isdesirable that such a force is avoided in retracting the tissue even ifan oxygen saturation value measured from the tissue may initially bewithin the desired oxygen saturation range. Such a force may be set as athreshold force value by the controller so that the positioningmechanism is prevented from applying the threshold force or any forcelarger than the threshold force.

A threshold force value may depend on many factors, such as tissue type,tissue size, temperature, and others. For example, a threshold forcevalue for a delicate tissue such as a nerve root is typically lower thana threshold force value for a skeletal muscle. When the force sensormeasures that a force applied to the retractor tip exceeds the thresholdforce value, then the controller sends a control signal to thepositioning mechanism so that the positioning mechanism moves in adirection that reduces a retraction force applied to the retractor tip.

Any suitable force sensor can be used in embodiments of the invention.For example, a force sensor can be a strain gauge load cell. The loadcell is a transducer that converts a force or load acting on it into anelectrical signal. When there are changes in the force or load cell,there will be a change in the electrical signal. Through a mechanicalarrangement, the force being sensed deforms a strain gauge along theaxis of the load cell. The strain gauge converts the deformation into anelectrical signal in proportion to the load. In embodiments of theinvention, one end of the load cell can be attached to a retractor(e.g., at its handle) and the other end of the load cell can be attachedto a positioning mechanism.

In another example, a force sensor can be a thin piezoresistive forcesensor. The piezoresistive force sensor is constructed of two substratelayers of polyester and polyimide film. Each layer has a conductivematerial, such as silver and a layer of pressure-sensitive ink. Then anadhesive is used to laminate the two substrate layers, forming a forcesensor. This piezoresistive force sensor is commercially available asFlexiForce® sensors from Tekscan (Boston, Mass.). The piezoresistiveforce sensor can be attached to a tip of a retractor (e.g., a retractorportion) which is used to contact and retract a tissue. When the tip ofthe retractor contacts and pulls aside a tissue, the pressure applied tothe tissue by the retractor tip is directly measured by thepiezoelectric force sensor at the point of contact.

Many other types of sensors can be connected to the retractor inembodiments of the invention. For example, a thermal sensor, positionsensor, visual sensor such as a camera, and others may be used, inaddition or in alternative to the previously mentioned sensors. Varioussensors in embodiments of the invention can provide input signals to thecontroller so that an appropriate control signal can be generated by thecontroller to move the positioning mechanism and the retractor.

Retractor 110 in embodiments of the invention can be used to retractvarious tissue types. For example, a retractor can retract a nervetissue (e.g., spinal cord, nerve root, facial nerve, peripheral nerve,and others), skeletal muscles, smooth muscles, nerve roots, connectivetissues, brain, lungs, kidneys, liver, stomach, intestines, ovaries,uterus, bladder, bone, prostate, thyroid, parathyroid, adrenal gland,pancreas, spleen, heart, and others. The size and shape of a retractorwill vary depending on the tissue type.

For example, a retractor for a skeletal muscle will be larger than aretractor for a nerve root. In one implementation of the invention, aretractor is a nerve retractor and a tissue to be retracted is a nerveroot, spinal cord, facial nerve, or peripheral nerve. Structural andfunctional properties of a nerve root retractor are described more indetail below and in FIG. 5 .

Positioning mechanism 130 in embodiments of the invention actuatesretractor 110. A positioning mechanism can be a device that comprisesone or more components, which are operatively linked together, and iscapable of moving another object that is attached to its component.Movement of the positioning mechanism can be controlled by a controlsignal produced by a controller. In addition, the positioning mechanismcan be controlled by a user input. For example, a component of thepositioning mechanism can be operatively connected to a joystick orstylus so that the user can manually manipulate movement of thepositioning mechanism.

In some embodiments, a positioning mechanism may include amacroactuation component to adjust a large movement of a retractor and amicroactuation component for a fine tuning of a retractor. For example,the macroactuation component of the positioning mechanism can place aretractor at a proper height and X-Y coordinate relative to a tissue sothat the retractor is ready to retract the tissue. The microactuationcomponent of the positioning mechanism can be used to pull or retractthe tissue according to a control signal provided by a controller.

In one implementation, a microactuation component of a positioningmechanism can include a linkage element connected to an actuator. Inthis embodiment, the linkage element is attached to a retractor. Thus,movement produced by the actuator is transferred to the linkage element,which in turn alters a position of the retractor.

A number of different types of linear actuators can be used in apositioning mechanism. These include a rotary motor with a lead screw,where the rotation of the motor rotates the screw, which in turn moves alinkage element attached to a nonmoving part of the rotary motor.Another type of actuator is a hydraulic actuator, where a hydraulicpressure displaces a hydraulic piston to achieve a linear movement. Apneumatic actuator can also be used, where air pressure displaces apiston to achieve a linear movement. These positioning mechanismsprovide a range of motion in a single axis, in a forward and reversedirection.

In another implementation, a positioning mechanism may further include amacroactuation component to initially position a retractor at a properlocation relative to a tissue to be retracted. For example, a platformwith a height adjustable supporting post can be used to adjust theheight of a retractor relative to a tissue to be retracted. Themacroactuation component allows the user to adjust the height of aretractor mechanically and eliminates a concern over unsteady hands orhand tremor of the user affecting the control of the retraction system.

Other suitable positioning mechanisms can be included to controlmovement of a retractor in embodiments of the invention. For example, aplanar magnetic levitation positioning system can be used. Typically, aplanar magnetic levitation positioning system includes a levitatedplatform which is suspended with no support other than magnetic fields.A retractor can be attached to a levitated platform, and its positioningcan be manipulated according movement of the levitated platform. Thissystem provides a six-degree-of-freedom for a retractor, where theretractor can move move forward/backward, up/down, left/right combinedwith rotation about three perpendicular axes. An example of a planarmagnetic levitation positioning system is described in, for example,U.S. Pat. No. 7,185,590, which is incorporated by reference along withall other references cited in the application.

Another positioning mechanism suitable in embodiments of the inventionincludes a robotic arm described in, for example, U.S. Pat. No.5,807,377, which is incorporated by reference. A retractor can beattached at one end of a robotic arm, and the retractor can bemanipulated by movement of the robotic arm.

In embodiments of the invention, controller 150 includes severalcomponents to handle input and output signals. For example, thecontroller includes a memory that stores algorithms or codes necessaryto process the input signals. The controller also includes a processorconfigured to rapidly execute the algorithms to produce a control signalto control movement of a positioning mechanism and a retractor.

The memory of the controller can be preloaded or preprogrammed withinformation regarding a desired or predetermined oxygen saturation valueor range, threshold force, and others. The memory can also bepreprogrammed with one or more lookup tables. For example, a lookuptable may correspond to the recorded measurements from an oximetersensor and contains a control signal request for the positioningmechanism appropriate for the detected oxygen saturation measurements.In another example, a lookup table may correspond to the recordedmeasurements from a force sensor and contains a command for apositioning system for the detected force measurements as determined bythe force sensor.

The controller may include one or more user interface devices thatenable the user to input data or various parameters. For example, thecontroller may include a keyboard or touch screen monitor that enablesthe user to input information into the controller regarding a patient,tissue type, desired or predetermined oxygen saturation value or rangefor a retracted tissue, threshold force values, and others. Thecontroller may also include a voice recognition system that enables theuser to input a command or data.

The controller may also include various output devices. For example, acontroller may include a display panel. A display panel may be used toshow a current oxygen saturation value of a retracted tissue, aretraction distance, or an amount of force that is applied to theretractor. The display panel can also display an elapsed time forretraction as well as data obtained at various time points. Thecontroller may also include a speaker or an alarm. The user can bealerted with an audible signal if the condition of a retracted tissue isat risk (e.g., low oxygen saturation level, low temperature, or tissuecolor change).

In addition to various components described above, the controller mayalso contain control circuits that control operation of various sensors.For example, the control circuits may send a signal, through opticalfibers or electrical wires, to an oximeter sensor or other sensors sothat the sensors measure parameters associated with a retracted tissue.The timing and frequency of sensor measurements can be preprogrammed orcan be input by the user.

In one embodiment, the control circuits may include signal emittercircuit and signal detector circuit. The signal emitter circuit mayoperate to send a signal through one or more optical fibers to theoximeter sensor. The signal detector circuit then receives a signal fromthe oximeter sensor via one or more optical fibers.

In some embodiments, the controller can include a first radiation sourceand a second radiation source. These radiation sources provide light foran oximeter sensor so that light can be transmitted into a retractedtissue and an attenuated version of the light can be received by adetector. In other embodiments, radiation sources can be locatedelsewhere, such as in a handle of the retractor, or in a separateenclosure.

In one implementation of the invention, a controller is a large,nonportable device that is attached to a wall or secured to a stand orsurface. In this implementation, the controller is typically connectedto AC power. A battery may be used to back up AC power. In anotherimplementation of the invention, a controller is a personal computer. Inanother implementation of the invention, a controller is a portableconsole that can be hand-carried by a user. A portable console canfollow a patient and measurements of tissue parameters can be madeanywhere in the hospital.

FIG. 2A illustrates a more detailed view of an embodiment of a retractorsystem. A retractor system 200 includes a retractor 210 which is used toretract a tissue, such as a nerve. Retractor 210 includes an oximetersensor 213 at its tip. Retractor system 200 also includes a positioningmechanism 220, which includes multiple components, to control positionand movement of the retractor. A force sensor 215 (e.g., a load cell)can also be included in the system to measure an amount of force that isapplied to the tissue by a tip of the retractor. System 200 furtherincludes a controller 240 which is connected to the positioningmechanism and the sensors.

Both oximeter sensor and force sensor are functionally connected tocontroller 240. A proximal end of retractor 210 includes a connector 214which connects the retractor to a cable 216. Cable 216 contains fiberoptic cables or electrical wires that functionally connect oximetersensor 213 to controller 240. Force sensor 215 has a cable 218 whichtransmits an electrical signal measured by the force sensor tocontroller 240, which is representative of the force measured.

In various implementations, controller 240 receives input signals fromoximeter sensor 213 or force sensor 215, or both. Based on the inputsignals from the sensors (one or both sensors), the controller producesa control signal which controls movement of the positioning mechanism220. In turn, the positioning mechanism adjusts a position of theretractor. Although this embodiment shows two sensors, in otherembodiments, there may be only one sensor, or more than two sensors, andthese can be used to control the positioning mechanism.

As shown in FIG. 2A, positioning mechanism 220 includes a microactuationcomponent and a macroactuation component. The microactuation componentincludes a linkage element 225 and a motor 230 connected together by agearing screw 235. Motor 230 can be a rotary driver where its rotationmakes the gearing screw to rotate. The screw has a continuous helicalthread around its circumference running along the length. Since linkageelement 225 is connected to a gearing screw, the rotation of the gearingscrew can be converted into usable linear displacement of the linkageelement. Retractor 210 can be attached to the linkage element so aposition of the retractor can be adjusted to retract a tissue accordingto movement of the motor.

The macroactuation component of positioning mechanism 220 includes aplatform with a height adjustable supporting post 250. This component ofthe positioning mechanism can be used support the microactuationcomponent (i.e., the linkage element and motor) so that the height ofthe retractor can be adjusted. By using the macroactuation component,retractor 210 can be placed in a suitable position relative to a tissueso that the retractor is ready to retract the tissue. If desired,however, the stand with a height adjustable supporting post 250 can beomitted and the retractor system can be handheld, or placed on a tableor other platform.

In one implementation of the invention, retractor 210 is directlyattached to linkage element 225. Retractor 210 has a shaft that iscurved in the middle, with a distal end having a tip to retract atissue. A proximal end of the shaft has a handle which can be connectedto linkage element 225. In this implementation, based on oxygensaturation of a tissue measured by oximeter sensor 213 at the tip of theretractor, the controller sends a control signal to actuate the linkageelement, which in turn adjusts a position of the retractor.

In another implementation of the invention, retractor 210 is indirectlyattached to linkage element 225 via force sensor 215. Force sensor 215can be a strain gauge load cell that has a first end 217 and a secondend 219 along its axis. First end 217 of the force sensor is attached toretractor 210 by clamp elements 223 and 224. Second end 219 of the forcesensor is attached to linkage element 225.

When linkage element 225 is pulled by motor 230, and retractor 210 movesin accordance with movement of the motor since it is connected to thelinkage element via force sensor 215. When a tissue is being pulledaside by the retractor tip by movement of the linkage element, there isa force or load acting on force sensor 215 along the horizontal axis ofthe load cell. The load or force measured by force sensor 215 isconverted into an electrical signal which is transmitted to controller240. The electrical signal is representative of an amount of force thatis applied to the tissue by the retractor tip. In this implementation,the controller can adjust movement of the retractor based on oxygensaturation measurements, force measurements, or both.

In embodiments of the invention, controller 240 receives severalfeedback or input signals from one or more sensors. For example, thecontroller receives information on oxygen saturation level of theretracted tissue from the oximeter sensor. The controller also receivesinformation on how much force is applied to the retractor which ismeasured by the force sensor. The controller also receives informationon a magnitude and direction of movement of the motor (and thus aretraction distance).

The controller may also receive input from the user. For example, theuser may provide input through input interface information on desiredoxygen saturation values or range, threshold force values, patientinformation, and others.

The controller processes various input signals and user input togenerate a control signal that controls movement of the motor. The inputsignals to and the control signals from the controller can becommunicated by wired connections or by any suitable wirelesscommunications.

FIG. 2B shows a flow diagram that illustrates a retractor system havinga closed loop control arrangement that can modulate a retraction forceapplied to a tip of a retractor based on a parameter of a retractedtissue measured by a sensor. Any suitable sensor can be used. Asdiscussed, an oximeter sensor is described merely as an example below;the sensor may be any type of sensor such as a force sensor or anothersensor described above.

In a step 260, a tissue is retracted to a selected retraction distanceby a retractor to expose the surgical site so that the surgeon can gainaccess to the surgical site.

In a step 265, an oximeter sensor included in the retractor measures anoxygen saturation value of the retracted tissue and transmits thisinformation to a controller.

In a step 270, the controller compares the measured oxygen saturationvalue of the retracted tissue with a first value and a second value,which are lower and upper threshold values of oxygen saturation,respectively. The first and second values may have system defaults (suchas set by the factory) or may be user defined (such as being input bythe user in a screen of a console). The values may be default valuesthat can be altered by the user.

If the measured oxygen saturation value of the tissue is above the firstvalue and below the second value (or equal to either values), then theretractor system maintains or holds a retraction force applied to theretractor tip (step 273).

In a step 275, if the controller determines that the measured oxygensaturation value of the tissue is below the first value, then theretractor system decreases a retraction force applied to the retractortip (step 277) to reduce stress on the retracted tissue. Consequently, aretraction distance of the tissue (i.e., a linear distance that thetissue is moved from its original position by the retractor tip at thepoint of contact) reduces also.

In step 280, if the controller determines that the measured oxygensaturation value of the tissue is above the second value, then theretractor system increases a retraction force applied to the retractortip (step 283). Consequently, a retraction distance of the tissueincreases also.

In step 280, if the controller determines that the measured oxygensaturation value of the tissue is below a second value (but above thefirst value), then the retractor system maintains or holds a retractorforce applied to the retractor tip (step 287).

As previously discussed, there may be multiple similar steps to steps270-280 for each additional sensor that is used to help position theretractor. There can be any number of such sensors, one, two, three,four, five, or more.

After steps 270, 275, or 280, the system loops back to step 265 tomeasure an oxygen saturation value of the retracted tissue. Bycontinuously cycling through these steps, an oxygen saturation value ofthe retracted tissue is constantly monitored and a retraction distanceof the tissue is adjusted accordingly so that oxygen saturation level ofthe retracted tissue can be maintained within a predetermined range,between the first value and the second value.

The user can input and set the first and second values of oxygensaturation at any suitable level, anywhere between 0 to 100 percent.Typically, the first value (a lower limit) is set at 20, 30, 40, or 50percent, and the second value (an upper limit) is set at 40, 50, 60, 70,or 80 percent. The second value will be set greater than the firstvalue.

The first and second values of oxygen saturation can be set differentlyby the user depending on many factors. These include tissue type,general health of a patient, duration of surgery, and others. For anexample, some tissues can tolerate a lower level of oxygen saturationduring surgery without resulting in tissue damage, where other tissuesmay be more sensitive and require a higher level of oxygen saturation.

Furthermore, oxygen saturation requirements for a tissue may changeduring surgery and can be set differently at different time point. Forexample, a nerve tissue may be able to withstand a lower oxygensaturation level during the first thirty minutes of surgery, butrequires a higher oxygen saturation level in the latter part of thesurgery. In such a circumstance, a threshold for oxygen saturationrequirements can be set lower during the first part of a surgery, and itcan be reset for the latter part of the surgery to avoid any permanentdamage to the tissue.

Further, the flow in FIG. 2B may also take into account an amount oftime (e.g., an elapse time) that the tissue has been retracted. Forexample, if the tissue has been retracted (such as a sensor output beingin a certain range) for more than X seconds (which may be referred to asretraction time). Then the retractor can reduce the retraction force togive the tissue Y seconds (which may be referred to as recovery time) torecover (e.g., allow full blood flow to a nerve). After recovery, thenthe retractor can again apply the previously applied force to thetissue.

The value of X or Y, or both, can be set by the system or there may be adefault value. X may be different from Y. Some sample values for X and Yare 5 seconds, 30 seconds, 60 seconds, 120 seconds, 360 seconds, 5minutes, 15 minutes, 30 minutes, or 60 minutes. For example, in oneimplementation, X is 5 minutes and Y is 30 seconds.

The elapsed retraction time may be shown on the console, so the doctorcan monitor during a procedure. The display may also show a countdown towhen a retractor enters into recovery mode, so the doctor can know howlong he has before he has to move his instruments away. By alsomonitoring retraction time in addition to oxygen saturation, forceapplied, and other sensor outputs, damage to tissue can be minimized.

Still further, the flow in FIG. 2B may take into account of a view fromvisual sensor, such as a camera, attached to a retractor system. Acamera can be used to determine, for example, whether there is a lack ofmotion or inactivity by a surgical team within its visual field at thesurgical site. When there is inactivity for more than X seconds orminutes, then the retractor system can reduce the retraction force togive the tissue time to recover until the camera detects motion withinits visual field. After detecting motion, then the retractor system canagain apply the previously applied force to the tissue.

In another example, a camera can be used as a visual sensor to determineif an amount of pooled blood surrounding a retracted tissue exceeds athreshold value. Pooled blood surrounding a retracted tissue caninterfere with accuracy of sensor measurements. For example, pooledblood may artificially increase oxygen saturation measurements of aretracted tissue measured from an oximeter sensor. When a camera detectsan amount of pooled blood exceeding a threshold value, oxygen saturationmeasurements from an oximeter sensor can be ignored. Alternatively,suction can be applied to remove pooled blood. This can be achieved byusing a retractor having an additional suction function or a separatesuction tool.

A camera can also provide an instant visual verification to the doctorwhether or not a retracted tissue is healthy. A retracted tissue mayfade or change color if it is under stress. Moreover, a camera can alsoalert the doctor if a retracted tissue is about to twitch or slip awayfrom the retractor.

In another aspect of the invention, a retractor device and system havingone or more sensors can be used without a closed loop controlarrangement (i.e., without a positioning mechanism). In some surgicalprocedures, the surgeon may wish to hold a retractor device by hand andhandle it manually, rather than having it automatically controlled by apositioning mechanism. Even without the use of a positioning mechanism,sensor measurements from the retractor system can guide the surgeon tomanipulate a retractor device in a manner that can preserve the healthof a retracted tissue during surgery.

FIGS. 3A-3D illustrate retractor devices which can be used eithermanually or with a positioning mechanism in a closed loop controlarrangement.

FIG. 3A illustrates a side view of a retractor device in accordance withone embodiment of the invention. The retractor device has a force sensor315 that is connected between a retractor 310 and a handle 318. Forcesensor 315 measures an amount of force applied to a tissue 325 (e.g., anerve) by a retractor tip 322 when handle 318 is pulled to the right toretract the tissue. A retractor portion 312 cradles tissue 325 so thatthe tissue is ready to be pulled, and a sensor 313 measures a parameterof tissue 325 at the point of contact. For example, sensor 313 can be anoximeter sensor that measures an oxygen saturation value of tissue 325at the point of contact.

FIG. 3B illustrates a top view of the same retractor device shown inFIG. 3A. As shown, the retractor device includes force sensor 315 whichis connected between retractor 310 and handle 318, ready to pull nerve325 resting near tip 322 of the retractor device.

In FIGS. 3A and 3B, when the retractor device is pulled by handle 318 ina horizontal direction to the right, nerve 325 is pulled away from itsoriginal, resting position to the right. The distance that nerve 325travels at the point of contact is referred to as a “retractiondistance,” shown as d_(r) in FIG. 3A. When handle 318 pulls theretractor device in a horizontal direction to the right, then nerve 325is pulled away from its original, resting position to the right, and aretraction distance of nerve 325 increases. When the retractor device isreturned back to the left, then a retraction distance decreases to apoint where the retraction distance equals zero as shown in FIGS. 3A and3B.

In one implementation, handle 318 can be held by hand, and the retractordevice can be used manually without a positioning mechanism. When thesurgeon pulls the handle and retracts tissue 325, force sensor 315measures a force which is applied to nerve 325 by retractor tip 322. Thesurgeon can monitor the force applied as well as other measurements oftissue parameters (e.g., oxygen saturation reading). Then the surgeoncan adjust a position of the retractor device, as necessary or desired,to keep a balance between a desired retraction distance and the healthof the tissue.

In another implementation, handle 318 shown in FIGS. 3A and 3B can beconnected to a positioning mechanism, such as a linkage elementconnected to an actuator. In this implementation, force sensor 315measures a force which is applied to nerve 325 by retractor tip 322 whena linkage element pulls handle 318 in a horizontal direction.

When a controller (not shown in FIG. 3 ) receives an input signal fromsensor 313, which is representative of a parameter of the retractedtissue, the controller can use this input signal to adjust a lineardistance that a tip of a retractor travels. A magnitude of this lineardistance will be proportional to the difference between the measuredparameter of the retracted tissue and a desired parameter level orrange.

For example, a desired or predetermined oxygen saturation range for atissue is preprogrammed to be between about 30 to 45 percent. A measuredoxygen saturation value of the tissue at time X is 50 percent, and ameasured oxygen saturation value of the tissue at time Y is 80 percent.The controller determines a difference between the measured oxygensaturation value and the desired oxygen saturation range. Since thisdifference is greater at time Y compared to at time X, then thecontroller will adjust a control signal so that a linear distance that aretractor tip travels will be greater at time Y compared to a lineardistance at time X.

The controller may also make adjustments to the positioning of theretractor in order to maintain the amount of force applied within adesired range (e.g., above a first value and below a second value). Theadjustments the controller makes may be a result of measurement of oneor two or more sensors.

For example, if a first sensor output is within a first desired range,and a second sensor output is not within a second desired range (whichmay be different from the first desired range), the controller will makepositioning adjustments to bring the second sensor output in range.Similarly, if a first sensor output is not within the first desiredrange, and the second sensor output is within a second desired range(which may be different from the first desired range), the controllerwill make positioning adjustments to bring the first sensor output inrange. If both the first and second sensor outputs are out of range, thecontroller will make positioning adjustments to bring both sensors intorange.

FIG. 3C shows another retractor device 330 which can be used with orwithout a positioning mechanism. Retractor device 330 has a first handle331, a shaft 333 connected at its proximal end 337 to the first handle,and a tip 335 connected to a distal end 339 of the shaft. The tipincludes a retractor portion or retractor blade 342 and an oximetersensor 343.

The shaft can include an internal channel or passageway. Optical fiberspass from sensor openings on the tip, through the channel, through thehandle, and into a cable jacket or cable insulation 345. Alternatively,the optical fibers can run along the shaft and secured by, for example,shrink wrap.

Retractor device 330 also includes a force sensor 346. Force sensor 346has a first end 348 and a second end 350 on the opposite side of thefirst end along the axis of force sensor s 346. Force sensor 346measures an amount of force that is applied in a horizontal directionalong its axis. First end 348 of force sensor 346 is connected to anL-shaped clamp element 352. L-shaped clamp element 352, together with alinear clamp element 354, is clamped to first handle 331 of theretractor device by a fastener 356. Second end 350 of force sensor 346is connected to a second handle 360. Force sensor 346 also has a cable358 (e.g., a metal wire) which transmits a signal measured by forcesensor 346 to a system unit (not shown).

Retractor device 330 can be used by placing oximeter sensor head 341 incontact with a tissue. Light is transmitted from a system unit or amonitoring console (not shown in FIG. 3C), through optical fiber incable 345, out a sensor opening on tip 335 and into the tissue. Thereflected light from the tissue is then received by another sensoropening on the tip, transmitted back to the monitoring console viaoptical fiber, and then processed. The monitoring console can displayoxygen saturation measurement. The monitoring console can also displayan amount of force that is applied to retract a tissue.

Retractor device 330 has two handles—first handle 331 and second handle360. When first handle 331 is used to retract a tissue, there is nochange in load or force for load cell 346 as it is not being pulledupon. When the tissue is retracted using first handle 331, oxygensaturation measurements of a retracted tissue can be made. However, aforce applied to a retracted tissue will not be measured.

When second handle 360 is used to retract a tissue, since the handle isconnected to load cell 346, a strain gauge in load cell 346 becomesdeformed as the surgeon pulls second handle 360 to retract a tissue. Theload or force measured by load cell 346 is converted into an electricalsignal which is transmitted to a system unit (not shown) via cable 345.When the tissue is retracted using second handle 360, both oxygensaturation and force measurements can be made.

While FIG. 3C illustrates an embodiment of the invention where the forcesensor is attached to a retractor as a separate unit and is pulled uponby a second handle, the force sensor can be an integral part of theretractor itself. For example, the force sensor can be located betweenfirst handle 331 and proximal end 337 of the shaft of the retractor. Inanother example, the force sensor can be located in the middle of shaft333. In yet another example, the force sensor can be located betweendistal end 339 of the shaft and retractor tip 335. When the force sensoris integrated as part of a retractor, second handle 360 can be omittedin the device, and first handle 331 can be used to retract or pull asidea tissue.

Further, while FIG. 3C shows the use of a load cell as a force sensor,other types of force sensors can be used at a different location ofretractor device 330. For example, a piezoresistive force sensor can beattached to a surface of retractor blade 342 that will be contacting atissue. As described above, such piezoresistive force sensor measures anamount of force that is applied from the tissue onto the force sensor.

Although the use of an oximeter sensor is described with FIG. 3C, thesensor may be any type of sensor (e.g., a thermal sensor, visual sensor,and others) described above. Further, there can be any number of suchsensors included in the retractor device shown in FIG. 3C.

FIG. 3D shows a photograph of mechanics of a system 370 including aretractor device similar to that shown in FIG. 3C. System 370 includes aretractor 371 with an oximeter sensor at its tip. A handle of retractor371 is connected to a load cell 375 by a clamp 373 at one end. Theopposite end of force sensor 375 is attached to an aluminum handle 377.Load cell 375 has a cable 379 which transmits an electric signal fromload cell 375 to an amplifier 385. The amplifier then amplifies theelectric signal from load cell 375 and transmits the signal to avoltmeter 383 which has an LCD display. Voltmeter 383 is connected to adata recorder 387 which can store force measurements and timing ofmeasurements.

The oximeter sensor located at the tip of retractor 371 is connected toa separate monitoring console (not shown in FIG. 3D) by a cable 380. Themonitoring console can display oxygen saturation measurements of aretracted tissue or provide an audible signal. As shown in FIG. 3D,force sensor measurements and oxygen saturation measurements can bedisplayed by separate displays. Alternatively, they can be combined intoa single console if desired.

FIG. 4 illustrates an implementation where a retractor system is usedwithout a closed loop control arrangement. Shown in FIG. 4 is a blockdiagram of a system 400 that includes a retractor device 410 and asystem unit 420. Retractor device 410 is used for retracting a tissue.Retractor device 410 can also be used to measure oxygen saturation ofthe retracted tissue and an amount of force applied to the tissue duringretraction. System unit 420 can process, display, and store informationprovided by retractor device 410.

Retractor device 410 has an oximeter retractor tip 403 which isconnected to a force sensor or load cell 406, which is in turn connectedto a handle 409. Oximeter retractor tip 403 includes a retractor portionwhich is used to retract a tissue and an oximeter sensor which is usedto measure oxygen saturation level of the tissue contacting the tip.Force sensor 406 measures an amount of force that is applied to thetissue by oximeter retractor tip 403 when a surgeon holds handle 409 andretracts or pulls aside the tissue.

System unit 420 has components that can process, display, and storeinformation provided by retractor device 410. For example, a first setof components—an amplifier circuit 421, display 422, and data recorder423—are functionally connected to load cell 406. A second set ofcomponents—oxygen saturation measurement circuit 425 and display 426—arefunctionally connected to oximeter retractor tip 403.

A signal from load cell 406 is transmitted to amplifier circuit 421,which amplifies the signal. Load cell 406 is a transducer that convertsa force or load acting on it into an electrical signal. When there arechanges in the force or load, there will be a change in the electricalsignal. The electrical signal output from the force sensor is small,typically in the order of a few millivolts, and is amplified byamplifier circuit 421.

Display 422 (e.g., an LCD monitor or a voltmeter) can digitally displaythe load cell output in real time. Data recorder 423 can save the forcesensor outputs and the time of measurements. For example, data recorder423 can be a USB data logger device that can be plugged into a USB port,such as on a personal computer. Data recorder 423 can save the forcesensor output once per second or at any other suitable rates, which maybe selected by the user.

In the second set of components of system unit 420, oxygen saturationsignals from oximeter retractor tip 403 are transmitted to oxygensaturation measurement circuit 425. Oxygen saturation measurementcircuit 425 processes and analyzes the signals using algorithms andconverts the signals into oxygen saturation values in terms ofpercentage. A display 426 is connected to oxygen saturation measurementcircuit 425 to show oxygen saturation values and the timing ofmeasurement. The oxygen saturation values, together with the time whenthe measurements were made, can be also stored in oxygen saturationmeasurement circuit 425, display 426, or other components not shown inFIG. 4 .

The components of system unit 420 can be enclosed in a single housing(e.g., a console or computer). Alternatively, they can be enclosed inseparate housings. For example, amplifier circuit 421 and display 422can be enclosed in a single housing, while data recorder 423 is enclosedin a separate housing. Furthermore, some of the components shown in FIG.4 can be combined into a single component. For example, display 422 anddisplay 426 can be combined into a single display panel.

The retractor devices and systems discussed so far describe how one ormore sensors can be connected to or integrated with retractor devices toprovide information regarding the state of the health of a retractedtissue. In FIG. 5 , shapes and materials for a nerve retractor with anoximeter sensor are described in detail. Also, FIGS. 6 through 19Cdescribe various patterns of oximeter sensor openings at the tip of aretractor. Retractors and oximeter sensor openings described below canbe combined with any other sensors (e.g., force sensor) or with apositioning mechanism described above.

While FIG. 5 provides details of a retractor for a nerve tissue, thediscussions about materials and oximeter sensor opening patterns can beapplied to retractors for any tissue type (e.g., liver, kidney, brain,muscle, pelvic organs, and others). The size and shape of a retractorcan be adjusted based on a tissue to be retracted, and sensors can beconnected to or integrated into various retractors as described in thisapplication.

FIG. 5 illustrates a more detailed view of one embodiment of aretractor, particularly useful for a nerve tissue. A retractor 555includes a shaft 558 with a proximal end 561 and a distal end 564. Theproximal end of the shaft is connected to a handle 567. The distal endof the shaft includes a tip 570 that has a retractor portion or blade571. Tip 570 also includes an oximeter sensor at the bottom surface ofthe tip near retractor portion 571.

A cable 573 may include one or more fiber optic cables or electricalwires enclosed in a flexible cable jacket. A connector 576 at one end ofcable 573 is connected to a connector 579 of retractor handle 567. Theother end of cable 573 (not shown) is connected to a controller, forexample via another connector, so that signals can be transmittedbetween the controller and the oximeter sensor (or other sensors).

In one embodiment, the shaft of the retractor is hollow, including aninternal channel or passageway 582 that runs the full length or someportion of the length of the shaft. The passageway may extend into thehandle. The passageway can be used to contain fiber optic cables,electrical wires, or combinations of both to functionally connect anoximeter sensor or other sensors to the controller.

In another embodiment, the shaft is a solid rod, and fiber optic cablesor electrical wires (electrically insulated in a cable) run along atleast some portions of the length of the shaft. These cables or wiresfunctionally connect the oximeter sensor and other sensors to acontroller. In the latter embodiment, the fiber optic cables orelectrical wires can be run along the shaft and secured by a jacket, forexample, shrink wrap.

In yet another embodiment, fiber optic cables or electrical wires thatrun to the sensor openings on the bottom surface of the retractor areencased in or sealed using an epoxy, adhesive resin, plastic, or othersimilar material or compound. The epoxy (or other material) holds thefibers or wires in place, and prevents damage to them. The shape of theepoxy or other material may be sculpted to facilitate ease in use of theretractor.

In one implementation, the tip of the retractor has one or more openingsat the bottom surface of the tip and has one or more fiber optic cablesinside the openings as an oximeter sensor. The fiber optic cables at thetip of the retractor can extend through the hollow shaft of theretractor and to cable 573, which is connected to the controller. Anemitter in the controller emits light which is transmitted through thefiber optic cables and out through openings in the tip of the retractorinto a tissue. The fiber optic cables may also be used to transmit thelight received from the tissue back to the controller.

In another implementation, an oximeter sensor may include radiationsources such as light emitting diodes (LED) and photodetectors which areplaced, for example, at the tip of a retractor. In this implementation,the passageway of the retractor shaft and the cable may containelectrical wiring to transmit power to the radiation sources.

The retractor shown in FIG. 5 can be connected to a positioningmechanism in any suitable manner. For example, handle 567 can beconnected to the positioning mechanism. In another example, proximal end561 of the shaft can be connected to the positioning mechanism. A handleof the retractor makes it convenient and comfortable for the surgeon tomanually hold the retractor during surgery. When a positioning mechanismis used to hold a retractor in embodiments of the invention, a handleportion of the retractor can be omitted if desired and the positioningmechanism can be attached to proximal end 561 of the retractor, or toany other suitable positions.

Although some specific dimensions, angles, and geometries, and retractorblades are shown and described in this application, one of skill in theart would understand that a retractor blade may be dimensioned or angleddifferently, so as to provide the appropriate control for the specificnerve or tissue being operated on. Further, the retractor may beadjustable such as having a variable length blade or a pivotable angleblade. Also, the retractor portion or blade may have different shapes,such as a hook.

Typically, the handle or the proximal end of the shaft is at an anglerelative to the rest of the shaft. For example, an axis 585 passeslongitudinally through the handle while an axis 588 passeslongitudinally through at least a portion the shaft. The two axes forman angle 592. In a specific implementation, angle 592 is 110 degrees.However, angle 592 may be 90 degrees (i.e., a right-angle), less than 90degrees (i.e., an acute angle), or greater than 90 degrees (i.e., anobtuse angle). Angle 592 typically ranges from about 90 degrees to about160 degrees. This includes, for example, 95, 100, 105, 110, 115, 120,125, 130, 135, 140, 145, 150, 155, 160, or more than 160 degrees.However, in an embodiment, the retractor has no angular differencebetween the handle and shaft (i.e., angle 592 is 180 degrees) andretractor is a straight puller.

The various angles allow the user to select an angle that the user ismost comfortable working with. For example, one user may prefer aretractor with a 90-degree angle because the user may find that at thatangle, the retractor is not sticking up towards the microscopeinterfering with vision and with the operating surgeon. In otherimplementations the shaft may be bendable by the user who can then shapethe shaft into any angle or configuration. In yet anotherimplementation, the shaft may include two or more pieces that arepivotally connected such as via screws and nuts. This too allows theuser to determine and set the desired angle and configuration.

In a specific embodiment, the shaft and handle may be detached andreattached by the user. This allows, for example, the user to select anangle for the retractor and use the same handle without having topurchase a whole new retractor. The shaft may be secured to the handleusing a threaded connection, a lug closure (e.g., twist and lock), apress fit, or combinations of these. In another embodiment, the shaftand the handle are secured using an adhesive or molded as a single unit.

In a specific implementation, the retractor has a shaft length L1 ofabout 120 millimeters and a handle length L2 of about 120 millimeters.However, these dimensions may vary widely depending on the application.

The shaft and other parts of the retractor may be made of any materialsuitable for use in surgery. In one embodiment, the shaft can be made ofmetal, such as steel, stainless steel, surgical stainless steel, gold,silver, rhodium, titanium, tungsten, aluminum, or combinations of theseor other suitable materials. The shaft may be an alloy of two or moreelements (e.g., iron, carbon, chromium, molybdenum, and nickel). Inanother embodiment, the shaft can be made of plastics, ceramics, orcomposites (e.g., carbon fiber). The shaft may also include acombination of materials such as steel surrounded by shrink-wrap tubing.

In an implementation of the present invention, the material of theretractor has suitable properties so that it does not interfere withsurgical procedures. For example, the material of the retractor is notreflective or minimally reflected. The retractor may be coated with anantireflective material (such as a block oxide coating) to make it lessreflective than the original starting material. Alternatively, theretractor may be processed (e.g., bluing, anodizing, or oxidizing),colored (e.g., black flat color), finished (e.g., matte finish), ortextured (e.g., bead-blasted finish) to reduce reflectivity. Reducingreflectivity of the retractor will reduce glare for the surgeon whenoperating. Moreover, reducing reflectivity of the retractor will ensurethat light which is transmitted into the tissue by an oximeter sensor isreceived back at detectors (which will be described below), instead ofbeing reflected off the retractor.

In another implementation of the present invention, the material of theretractor is not electrically conductive or has reduced electricalconductivity compared to the original starting material. Because theretractor can be used to retract tissues including nerves, it may not bedesirable to shock the nerves with electrostatic energy accidentally.The retractor may be made from material that is not conductive such as aceramic, plastic, or resin. Alternatively, the retractor may includeinsulating material inserted between the tip (which touches the nerve)and the proximal end or other portions of the retractor.

In another implementation of the present invention, the material of theretractor is not thermally conductive or has reduced thermalconductivity compared to the original starting material. Because theretractor is used to retract nerves, temperature changes in theretractor can be propagated to the nerve quite quickly. It is generallydesirable not to thermally heat the nerve or else it may become damaged.So, the retractor may be made from material that is not thermallyconductive such as a ceramic, plastic, or resin. Alternatively, theretractor may include thermally insulating material inserted between thetip (which touches the nerve) and other portions of the retractor.

FIG. 6 shows a right-hand side view of a retractor tip 605. A left-handside view of the tip is a mirror image of what is shown in FIG. 6 . Tip605 is connected to a distal end 610 of the shaft. The tip includes aretractor portion or blade 615 and a bottom surface 645. The blade is atan angle relative to the shaft and to the bottom surface. Also includedat the bottom surface 645 of the tip 605 is an oximeter sensor 660. Theoximeter sensor can be located at any suitable location as long as itcan contact a tissue during retraction. For example, the oximeter sensorcan be located at blade surface 631 or at the bottom surface 645 nearthe blade surface as shown in FIG. 6 .

The tip has a thickness as shown by a distance of y44. In a specificimplementation, the thickness is about 2 millimeters. However, thethickness may range from about 1.5 millimeters to about 5 millimeters.In some embodiments, the thickness will be less than 1.5 millimeters.

Generally, a smaller thickness (or thinner profile) is desirable toallow, for example, a smaller incision to be made. A smaller incisionallows for faster healing and less scarring. Patients may alsoexperience fewer infections.

Blade surface 631 may be flat, as shown, or angled (e.g., concave orconvex) or have another contour (e.g., ogee, French curve, arch, orhook) as desired for the particular operation or intended use. Thevarious contours on the blade surface may be part of a blade that alsohas one or more contours in other dimensions or planes.

For example, blade surface 631 may have a concave blade surface (from aside view as shown in FIG. 6 ), allowing the blade to gently cradle aportion of a round perimeter of a nerve as it is retracted. The stressesaround the perimeter of the nerve may be more evenly distributed whichmay help prevent the nerve from traumatically creasing, folding, orcompressing.

In a specific implementation, the blade surface may also have a texturedsurface. For example, the surface may include multiple nubs, bumps,ribs, or protrusions. These surface features may help to lift portionsof the nerve away from the blade surface so as to minimize any crushingof blood vessels running alongside the nerve or to promote aeration ofthe nerve.

In another implementation, the blade surface may have multiple holes topromote, for example, aeration of the nerve while it is being retracted.

In yet another implementation, blade surface 631 may have a convex side(when viewed from bottom along axis 630) in addition to concave surface(when viewed from side as shown in FIG. 6 ). Like the concave surface,the convex side has similar benefits. That is, as the nerve is beingretracted, there will be less pinching (i.e., high pressure points orrelatively higher force per unit area) at the outermost points of thearc or crescent. An arc shape generally reduces the number of highstress points when retracting a nerve.

Referring now to FIG. 6 , bottom surface 645 may be flat, as shown, orhave another contour as desired for the particular operation or intendeduse. For example, the bottom surface may have a concave region tosimilarly cradle the nerve and distribute stress as blade surface 631.The bottom surface may also be textured (e.g., nubs, bumps, ribs, andprotrusions) to lift portions of the nerve away from the bottom surfaceso as to minimize any crushing of blood vessels running alongside thenerve or to promote aeration of the nerve.

An axis 620 passes longitudinally through the shaft. In this specificimplementation, bottom surface 645 is a flat plane that is parallel toaxis 620, but this is not necessarily the case for other implementationsof the retractor.

An axis 630 passes through a blade surface 631 and intersects axis 620.In this specific implementation, blade surface 631 is flat, but this isnot necessarily the case for other implementations of the retractor. Theblade surface is angled (i.e., angle 640) relative bottom surface 645and axis 620.

In a specific implementation, angle 640 is about 90 degrees. However, asdiscussed above, the specific angle may vary. Typically, angle 640ranges from about 90 degrees to about 179 degrees. For example, theangle may be about 100, 110, 120, 130, 135, 140, 150, 160, 170, or morethan 179 degrees, such as 180 degrees. In other implementations, theangle is less than 90 degrees.

The various angles accommodate the preferences of different users andintended uses for the retractor. For example, during spinal surgery theuser uses the blade to retract the nerve off to one side so that thesurgeon can work on the disc without damaging the nerve. Some users mayprefer to retract the nerve using a downward motion and then pulling thenerve to the side. For these users, a 90-degree blade may beappropriate.

Other users may prefer to retract the nerve using both a downward andsideways motion. For these users, a blade with an angle to the shaftgreater than 90 degrees, such as 130 degrees may be more appropriatethan a blade having a 90-degree angle. Further, the angle of the blademay be helpful in preventing too much force from being applied to anerve, which may possibly damage the nerve or tissue.

Further, as shown above, the blade is angled relative to the bottomsurface of the tip. But this angle is not necessarily the same angle asbetween the blade and the axis of the shaft. For example, in someimplementations of the invention (which are not shown), the bottomsurface of the tip may be perpendicular (or at another angle) relativeto the axis of the shaft. Then, the blade would be angled relative tothe bottom surface, but parallel to the axis of the shaft.

The blade is angled relative to the bottom surface. In a specificimplementation, this angle is about 90 degrees. However, this angle mayrange from about 90 degrees to about 179 degrees. For example, thisangle may be about 100, 110, 120, 130, 135, 140, 150, 160, 170, or morethan 179 degrees, such as 180 degrees. In other implementations, theangle is less than 90 degrees.

FIGS. 7 through 10 illustrate various patterns of source structures anddetector structures in an oximeter sensor located at a bottom surface atthe tip of a retractor. An oximeter sensor measures oxygen saturation ofa tissue. In embodiments of the invention, the oximeter sensor islocated at a tip of a retractor, where it can contact and measure oxygensaturation level of a retracted portion of the tissue.

Each oximeter sensor comprises at least one source structure and atleast one detector structure. A source structure is a structure in theoximeter sensor that provides light that can be transmitted into atissue. The source structure can generate the light, or it can be astructural component that transmits the light generated elsewhere (e.g.,from an upstream source). A detector structure is a structure in theoximeter sensor that detects light (or that is a structural component ofthe detection process) which is scattered and reflected from the tissue.

Typically, a source structure emits light (i.e., electromagneticradiation) of one or more specific wavelengths in visible or infraredrange suitable for monitoring oxygen saturation of a tissue. Forexample, a source structure can provide light having a wavelength fromabout 600 nanometers to about 900 nanometers. In one embodiment, asource structure emits light having a wavelength of 690 nanometers intoa tissue, and a detector structure can receive an attenuated version ofthe light of the same wavelength after the light has been scattered andreflected from the tissue. In another embodiment, a source structureemits light having a wavelength of 830 nanometers, and the detectorstructure can receive an attenuated version of the light of the samewavelength.

In some embodiments, the source structures (e.g., radiation sources) maybe dual wavelength light sources. In other words, first radiation sourceprovides two wavelengths of radiation and second radiation sourceprovides two wavelengths of radiation. First radiation source, secondradiation source, or both may produce light in any wavelength, buttypically the wavelengths range from about 600 nanometers to about 900nanometers. In a specific implementation a first wavelength of light isgenerated that has a wavelength of about 690 nanometers. A secondwavelength of light is generated that has a wavelength of about 830nanometers.

In one implementation, a source structure can be a laser or lightemitting diode (LED) that emits a light of a specific wavelengthsuitable to monitor oxygen saturation. A detector structure can be aphotodiode (e.g., a PN diode, a PIN diode, an avalanche diode, and soforth) that detects the light transmitted and reflected from a tissue,after the source structure emits the light into the tissue. In anoximeter sensor, both LEDs and photodiodes are located at the scanningsurface of the oximeter sensor. These LEDs and photodiodes can then beelectrically connected to a system unit which will be described below.In this implementation, since the light is generated next to the tissuesurface and subsequently detected at the tissue surface, there is lessattenuation of a signal.

In another implementation, a source structure is an opening in anoximeter sensor (at its scanning surface) with an optical fiber inside,which is connected to a signal emitter located elsewhere (e.g., systemunit). Likewise, a detector structure is an opening in an oximetersensor (at its scanning surface) with an optical fiber inside, which isconnected to a signal detector located elsewhere. The optical fibersfrom each oximeter sensor are then connected to either an emitter or adetector which may be located in a system unit.

Each of FIGS. 7 through 10 shows a particular opening pattern. Theopenings in the figures can be either source structures or detectorstructures, and they may be referred to herein as an opening or openingsin FIGS. 7 through 10 . The figures show only some examples of openingpatterns, other opening patterns may be used with embodiments of theinvention.

FIG. 7 shows a bottom view of a tip 705 with two openings, a singlelight source and single detector in a symmetrical array. In theimplementation shown in FIG. 7 , the tip has two openings. A firstopening includes a source structure 711. A second opening includes adetector structure 714.

In one embodiment, the source and detector structures generally includeoptical fibers that are used to measure oxygen saturation levels intissue, such as a nerve. In an implementation, optical fiber is usedhaving a diameter of about 1 millimeter, but other diameter fibers maybe used, including 0.5 millimeter, 0.75 millimeter, 2 millimeters, 3millimeters, 4 millimeters, 5 millimeters, and larger sizes.

The source structure typically includes an end of a first optical fiberwhere the opposite end of the first optical fiber is connected to alight source. The detector structure typically includes an end of asecond optical fiber where the opposite end of the second optical fiberis connected to a photodetector.

In a specific implementation, the source and detector structures are ina symmetrical arrangement. For example, each source and detectorstructure has a reference point. The reference point may be the centersof the sources and detectors if, for example, the sources and detectorshave circular shapes. Alternatively, the reference point may be definedas some other point, so long as the definition is consistent among thesources and detectors.

Lines 717 and 723 pass through the source and detector structures. Line717 is parallel to a y-axis 720 b and passes through the reference pointof source structure 711. Line 723 is parallel to y-axis 720 b and passesthrough the reference point of detector structure 714. Lines 717 and 723are coincident. That is, source structure 711 is in a symmetricalarrangement with respect to detector structure 714.

A line 726 is parallel to an x-axis 720 a and passes through thereference point of the detector structure. A line 729 is parallel tox-axis 720 a and passes through the reference point of the sourcestructure. Source structure 711 and detector structure 714 are separatedby a distance y1 between lines 726 and 729.

The separation between the source and detector structures may varywidely. By way of example, distance y1 is about 1.5 millimeters. Asmaller distance y1 helps to contribute to a smaller tip size. Smallertip sizes are generally desirable because they allow the use of smallerincisions. In turn, a smaller incision allows for faster healing andless scarring. Patients may also experience fewer infections.

However, in another implementation, distance y1 is about 5 millimeters.Distance y1 generally ranges from about 1.5 millimeters to about 5millimeters. For example, distance y1 may be about 1.5, 2, 2.5, 3, 3.5,4, 4.5, 5, or more than 5 millimeters. In other implementations,distance y1 may be less than 1.5 millimeters.

Larger source-detector separations may allow, for example, the detectorstructures to detect light after the light has penetrated deeper intothe tissue.

In a specific implementation where fiber optic cables are included, thesize of the fiber optic cable may vary. In a specific implementation,where fiber optic cables having circular cross sections are used, thediameter of a fiber optic cable end at the source structure, detectorstructure, or both is approximately 0.5 millimeters, but may range fromabout 0.5 millimeters to about 3 millimeters. For example, the diametermay be about 0.5, 1, 1.5, 2, 2.5, 3, or more than 3 millimeters. Inother implementations, the diameter of the fiber optic cable may be lessthan 0.5 millimeters.

Generally, the diameter of the fiber optic cable and correspondingopening will be about the same. Smaller openings allow, for example,smaller tips. Larger openings, allow, for example, more light to betransmitted into the tissue, and received from the tissue.

A distance x1 is between line 723 and an edge 732. That is, the sourceand detector structures may be offset by distance x1 from edge 732. Edge732 marks the base of a retractor portion or blade 735. The source anddetector structures are typically placed close to edge 732 such thatdistance x1 is at least about 0.5 millimeters. However, distance x1 mayvary from about 0.5 millimeters to about 3 millimeters depending on theapplication.

Typically, the source and detector structures are located closer to theretractor portion as opposed to the distal end of the shaft. Forexample, a line 740 that is parallel to the y-axis passes through thedistal end of the shaft.

A distance x2 is between lines 740 and 717. Generally, distance x2 willbe greater than distance x1. In a specific implementation, distance x2is about 4.8 times greater than distance x1. However, distance x2 mayrange from about 3 to about 6 times greater than distance x1. Forexample, distance x2 may be 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3,4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, or more than5.5 times greater than distance x1. In other implementations, distancex2 may be less than 3 times greater than distance x1.

The variations of the relationship between distance x2 and distance x1reflects the varying dimensions of a nerve or other linear tissue. Forexample, the diameter of a nerve may vary from patient-to-patient. Itmay also vary along the length of a nerve. The diameter of a nerve mayrange from about 1 millimeter to about 5 millimeters. For example, thenerve root in the lower back of a typical adult is about 4 millimetersin diameter. Because the nerve is typically retracted using the blade,locating the source and detector structures near edge 732 allows lightto be transmitted from the source structure into the nerve and thenreceived by the detector structure.

Generally, distance x1 will be proportional to the size of the nerve.That is, smaller nerves will result in a smaller distance x1 whilelarger nerves will result in a larger distance x1. Since nervesgenerally have circular cross-sections, this dimensional relationshiphelps to ensure, for example, that the source and detector structuresare placed over the thickest part of the nerve, i.e., over the diameterof the nerve, when the nerve is pulled by the hook.

For example, where the nerve is small, such as the nerve of a child, thesource and detector structures may be located closer to edge 732 so thatthe source and detector structures will be located above the nerve.Thus, light can be transmitted into the nerve and received from thenerve. Where, however, the nerve is large, such as the nerve of anadult, the source and detector structures may be located further awayfrom edge 732.

Typically, the source and detector structures are located along one ormore axes that are parallel to the longitudinal edge of the retractorportion. This allows, for example, measurements of linearly-shapedtissue such as a nerve. For example, line 717, which passes through thesource and detector structures, is parallel to edge 732 of the retractorportion. During use, the nerve is typically situated against edge 732.The longitudinal axis of the nerve is then parallel to edge 732.Locating the source and detector structures along axes parallel to edge732 helps to ensure that the nerve will be located below the source anddetector structures.

A distance x3 is from line 723 to an outside edge of the blade. In aspecific embodiment, distance x3 is about 1.75 millimeters. However,distance x3 may vary depending on the application including, forexample, the material that the retractor is made of. For example, amaterial with a relatively high strength may allow for a thin blade(i.e., a shorter distance x3). However, a material with a lower strengthmay require a thicker blade (i.e., a longer distance x3) so that theblade is more durable, making harder to break or bend.

In a specific embodiment, the source and detector structures may belocated on the blade. The source and detector structures may havesimilar positions, configurations, arrangements, shapes, designs,measurements, and spacings as they would have if placed on the bottomsurface of the tip as discussed in this application. Furthermore, aspecific embodiment may include a combination of source structures,detector structures, or both that are located on the blade and bottomsurface of the tip.

One advantage of locating the source structures, detector structures, orboth on the blade is that it may allow for a measurement (e.g., oxygensaturation measurement) to be made without the tissue having to contactor be positioned close to the bottom surface of the tip. For example,there may be some situations where the user is unable to fully insertthe blade into the incision such that when the tissue is retracted thesensors on the bottom surface are close enough to the retracted tissuethat a measurement can be made. However, sensors located on the blademay be close enough to the tissue to make the measurements.

In another implementation, the arrangement of source and detectorstructures is asymmetrical. An asymmetrical arrangement of source anddetector structures is discussed in U.S. Pat. No. 7,355,688, which isincorporated by reference. Any of the asymmetrical arrangements ofsource and detector structures discussed in that patent is applicable tothe sources and detectors in this application.

For example, FIG. 8 shows a bottom view of a tip 805 with threeopenings, one light source and two detectors in an asymmetrical array.In the implementation shown in FIG. 8 , the tip has three openingsarranged on a line. A first opening includes a source structure 811.Second and third openings include detector structures 814 a and 814 b,respectively.

A line 817 which is parallel to a y-axis 820 b passes through thereference point for each of the source and detector structures. A line823 which is parallel to an x-axis 820 a passes through the referencepoint of source structure 811. A line 826 which is parallel to thex-axis passes through the reference point of detector structure 814 a. Aline 829 which is parallel to the x-axis passes through the referencepoint of detector structure 814 b.

The asymmetrical source and detector array of FIG. 8 includes sourcestructure 811 and detector structure 814 b, with detector structure 814a interposed between source structure 811 and detector structure 814 b.Source structure 811 and detector structure 814 b are located atopposite ends of the array, while detector structure 814 a is located ina middle, but off-center portion of the array.

For example, a distance y10 is between lines 823 and 826. A distance y11is between lines 826 and 829. Distance y10 is different from distancey11. Although distance y10 is shown as being greater than distance y11,it should be appreciated that distance y11 may instead be greater thandistance y10. The difference between distance y10 and distance y11 isgenerally characteristic of the offset arrangement, or substantiallyunbalanced arrangement of the source structure relative to the detectorstructures.

A distance y12 is between lines 823 and 829. In a specificimplementation, distance y11 is about one-third of the distance y12 anddistance y10 is about two-thirds of the distance y12. For example, ify12 is 5 millimeters then y11 is 5/3 millimeters and y10 is 10/3millimeters (i.e., ⅔ *5 millimeters is 10/3 millimeters).

However, other implementations may include a symmetrical source-detectorarrangement. For example, distance y10 may equal distance y11.

FIG. 9 shows a bottom view of a tip 905 with four openings, two lightsources and two detectors in a symmetrical array. In the implementationshown in FIG. 9 , the tip has four openings arranged on a line. Firstand second openings include source structures 911 a and 911 b,respectively. Third and fourth openings include detector structures 914a and 914 b, respectively.

A line 917 which is parallel to a y-axis 920 b passes through thereference point for each of the source and detector structures. A line923 which is parallel to an x-axis 920 a passes through the referencepoint of source structure 911 a. A line 924 which is parallel to x-axis920 a passes through the reference point of source structure 911 b. Aline 926 which is parallel to the x-axis passes through the referencepoint of detector structure 914 a. A line 929 which is parallel to thex-axis passes through the reference point of detector structure 914 b.

The two light source and two detector array of FIG. 9 includes sourcestructure 911 a and detector structure 914 b located at opposite ends ofthe array, while source structure 911 b and detector structure 914 a areinterposed between source structure 911 a and detector structure 914 b.That is, the arrangement shown in FIG. 9 provides the furthestseparation between a source and detector structure (i.e., 911 a and 914b) by locating them on opposite ends of the array.

Separating source structure 911 a and detector structure 914 b as far aspossible has advantages over other arrangements that may locate thesource structures on opposite ends of the array with the detectorstructures interposed between. One advantage is that the light emittedfrom source structure 911 a can travel deeper into the tissue before itis received by detector structure 914 b. Another advantage is that thetip may be constructed with a very small size and therefore can be usedin clinical applications where smaller instruments are advantageousbecause only a small incision is required to use them. Applicationsinclude, for example, spinal nerve root oxygenation measurement andmonitoring in digit replantation.

In a specific implementation, the two-light-source and two-detectorarray is symmetrical. That is, the spacing between adjacent sources anddetectors is equal. For example, a distance y20 is between lines 923 and924. A distance y21 is between lines 924 and 926. A distance y22 isbetween lines 926 and 929. A distance y23 is between lines 923 and 929.

In a specific implementation, distances y20, y21, and y22 are the same.In a specific implementation, distances y20, y21, and y22 are eachone-third the distance y23. For example, if y23 is 5 millimeters theny20, y21, and y22 are all 5/3 millimeters.

FIG. 8 described a lack of symmetry in the positioning of source anddetector structures such that distances between source and detectorstructures varied relative to a y-axis. However, a lack of symmetry mayinstead or additionally have a lack of symmetry relative to an x-axis.Referring next to FIG. 10 , a tip that includes a detector structure inan offset arrangement relative to a set of source structures and adetector structure will be described.

FIG. 10 shows a bottom view of a tip 1005 with four openings, where atleast one of the openings is not aligned or asymmetrical with the otheropenings. In this figure, there is one opening that is not aligned withthe openings. In another implementation, there are two openings that arenot aligned with the other openings. In another implementation, thereare at least three openings that are not aligned to each other. Inanother implementation, there are at four openings that are not alignedto each other.

A specific implementation of the figure has two light source and twodetectors in an asymmetrical array. In the implementation shown in FIG.10 , the tip has four openings with three openings arranged on the sameline and a fourth opening arranged offset from the line. First andsecond openings include source structures 1011 a and 1011 b,respectively. Third and fourth openings include detector structures 1014a and 1014 b, respectively. The tip also includes a bottom surface 1015and a retractor portion or blade 1016.

A line 1017 which is parallel to a y-axis 1020 b passes through thereference point for source structures 1011 a and 1011 b and detectorstructure 1014 a. A line 1018 which is parallel to y-axis 1020 b passesthrough the reference point for detector structure 1014 b.

A line 1023 which is parallel to an x-axis 1020 a passes through thereference point of source structure 1011 a. A line 1024 which isparallel to x-axis 1020 a passes through the reference point of sourcestructure 1011 b. A line 1026 which is parallel to the x-axis passesthrough the reference point of detector structure 1014 a. A line 1029which is parallel to the x-axis passes through the reference point ofdetector structure 1014 b.

A distance y30 is between lines 1023 and 1029. A distance y32 is betweenlines 1023 and 1024. A distance y34 is between lines 1024 and 1026. Adistance y36 is between lines 1026 and 1029.

Lines 1017 and 1018 although parallel to the y-axis are not coincident.That is line 1017 is offset from line 1018 by a distance x10 along thex-axis, i.e., there is a lack of symmetry with respect to the x-axis. Ina specific implementation x10 is about 0.5 millimeters. However, x10 mayrange from about 0.1 millimeters to about 2.5 millimeters. For example,x10 may be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3,1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5 or more than2.5 millimeters. In other implementations, x10 may be less than 0.1millimeters.

As a further example, in an asymmetrical arrangement, the sources anddetectors are arranged so there is a first distance between a firstsource structure (e.g., 1011 a) and a first detector structure (e.g.,1014 a) and a second distance between the second source structure (e.g.,1011 b) and a second detector structure (e.g., 1014 b), where the firstand second distances are not equal.

For example, in a specific implementation, the distance along the y-axisbetween adjacent sensors is

$\frac{n}{\left( {m - 1} \right)},$where n is the distance along the y-axis between the furthest source anddetector pair and m is the number of sensors. Thus, in a specificimplementation including four sensors and a y-axis distance of 5millimeters between the furthest source and detector pair, the y-axisdistance between adjacent sensors is 5/3 millimeters (i.e.,

$\left. {\frac{5{millimeters}}{\left( {4 - 1} \right)} = {\frac{5}{3}{millimeters}}} \right).$

In this example then, the first distance (i.e., source structure 1011 ato detector structure 1014 a) is 10/3 millimeters (i.e., 3.3millimeters). The second distance (i.e., source structure 1011 b todetector structure 1014 b) is 3.4 millimeters, where x10 is 0.5millimeters (i.e.,

$\left. {{{second}{distance}} = {\sqrt{(0.5)^{2} + (3.3)^{2}} = 3.4}} \right).$

The bottom surface is generally planar with one or more openings throughwhich light is transmitted into the tissue and received from the tissue.However, in other implementations, the bottom surface may not be planar.For example, the bottom surface may have a convex surface, a concavesurface, or both convex and concave regions.

In a specific implementation, the bottom surface may have the shape of arectangle. However, this is not always the case. The bottom surface mayhave any shape. For example, in an implementation, the bottom surfacemay have the shape of a different type of polygon such as a square,rectangle, triangle, and parallelogram, or have a shape composed ofcurved line segments (e.g., oval, ellipse, and crescent), orcombinations of these (e.g., semicircle).

Typically, the surface area of the bottom surface will be larger thanthe surface area of the openings. For example, the surface area of thebottom surface may be about two-hundred and fifty to about three-hundredand fifty times greater than the combined surface area of the openings.In other implementations, the surface area of the bottom surface will beless than or equal to the surface area of the openings.

In a specific implementation, the bottom surface has a length x20 and awidth y40. In a specific implementation, such as a single source andsingle detector array, the bottom surface has a width of about 3millimeters and a length of about 5 millimeters. In anotherimplementation, such as with additional sources and detectors (e.g.,two-source and two-detector array), the bottom surface may have agreater width such as 8 millimeters. Table A below showsdimensions—length x20 (FIG. 10 ), width y40 (FIG. 10 ), and thicknessy44 (FIG. 6 )—for various implementations of the invention, and also arange of dimensions. However, it should be noted that these dimensionsmay vary greatly depending upon the application.

TABLE A First Second Third Range of Implemen- Implemen- Implemen-Dimensions tation tation tation (milli- Dimension (millimeters)(millimeters) (millimeters) meters) Length (x20) 5 17.5 17.5 2.5-20Width (y40) 3 8 8   2-20 Thickness (y44) 2 3 5  2-5

FIGS. 11 through 15 illustrate additional variations of sensor openingpatterns at a bottom surface of a retractor tip, where a retractorportion at the tip has an edge profile other than a straight line.

FIG. 11 shows a bottom view of an embodiment of a tip 2205. In thisexample, a retractor portion 2210 has an edge profile having a slightarc or crescent. A convex side 2215 of the arc is positioned near alinear source-detector array 2220. A concave side 2225 of the arc isopposite the convex side.

One advantage of the convex side of the retractor portion is a moreuniform distribution of stresses across the length of the nerve as it isbeing retracted. That is, as the nerve is being retracted, then therewill be less pinching (i.e., high pressure points or relatively higherforce per unit area) at the outermost points of the arc or crescent. Anarc shape generally reduces the number of high stress points whenretracting a nerve. However, in other implementations, other edgeprofiles and shapes may be used including having the concave side of thearc positioned on the side of the source-detector array.

In the example shown in FIG. 11 , the source-detector array isapproximately tangent to convex side 2215. That is, the source-detectorarray is arranged on a line as opposed to a curve. In this embodiment, adistance from a source structure, detector structure, or both to convexside 2215 may vary. For example, a first distance from source structure2230 a to the convex side is different from a second distance fromsource structure 2230 b to the convex side. In a specificimplementation, the first distance is greater than the second distance.However, in another implementation the first distance may be less thanthe second distance. This may be the case, for example, when the concaveside of the retractor portion is positioned on the side of thesource-detector array. It may also be the case when the sourcestructures, detector structures, or both are in an offset arrangement,i.e., not all of the source and detector structures are arranged on thesame line.

Furthermore, in a symmetrical source-detector arrangement, one side(e.g., top half) is a mirror image of another side (e.g., bottom half).For example, in FIG. 11 an axis 2240 running longitudinally through theshaft divides the bottom surface into a top half and bottom half. Thetop half and bottom half are mirror images of each other. A thirddistance from detector structure 2235 a to the convex side is equal tothe second distance (i.e., source structure 2230 b to the convex side).Likewise, a fourth distance from detector structure 2235 b is equal tothe first distance (i.e., source structure 2230 a to the convex side).

The radius of the crescent-shaped retractor portion may be constant, asshown in FIG. 11 , or it may be increasing or decreasing. For example,in a specific implementation, the radius increases from source structure2230 a to detector structure 2235 b. Thus, a first distance from sourcestructure 2230 a to the convex side will be greater than a seconddistance from source structure 2230 b to the convex side. The seconddistance will be greater than a third distance from detector structure2235 a to the convex side. The third distance will be greater than afourth distance from detector structure 2235 b to the convex side.

As another example, the radius may be decreasing from source structure2230 a to detector structure 2235 b. Thus, a first distance from sourcestructure 2230 a to the convex side will be less than a second distancefrom source structure 2230 b to the convex side. The second distancewill be less than a third distance from detector structure 2235 a to theconvex side. The third distance will be less than a fourth distance fromdetector structure 2235 b to the convex side.

In another embodiment, the source-detector array may be arranged on acurve. The curve may match the curve of the convex side of the retractorportion. Thus, a first distance from source structure 2230 a to theconvex side will equal a second distance from source structure 2230 b tothe convex side. A third distance from detector structure 2235 a to theconvex side will equal a fourth distance from detector structure 2235 bto the convex side.

FIG. 11 also shows another example of a geometric arrangement of sourcestructures 2230 a and 2230 b and detector structures 2235 a and 2235 b.In this first geometric arrangement, a first distance between a firstsource structure (i.e., 2230 a) and a second source structure (i.e.,2230 b) is different from a second distance between the second sourcestructure (i.e., 2230 b) and a first detector structure (i.e., 2235 a).The second distance may be larger than the first distance. Furthermore,a third distance between a second detector structure (i.e., 2235 b) andthe first detector structure may be equal to the first distance.

However, many other different geometric arrangements are possible. Forexample, in a second geometric arrangement, the first, second, and thirddistances are equal. In a third geometric arrangement, the seconddistance is less than the first distance, third distance, or both. Thefirst and third distances are equal. In a fourth geometric arrangement,the third distance is greater than the first distance, second distance,or both. The first and second distances are equal. In a fifth geometricarrangement, the first distance is greater than the second distance,third distance, or both. The second and third distances are equal.

FIG. 11 shows various geometric arrangements of source and detectorstructures relative to a single axis where the source and detectorstructures were all arranged on a line. However, other geometricarrangements may instead or additionally have distances between sourceand detector arrangements relative to a second axis.

For example, FIG. 12 shows another example of a geometric arrangementhaving distances relative to an x-axis. This specific example includesfour sensors including source structures 2310 a and 2310 b and detectorstructures 2315 a and 2315 b. A first distance is between a first sourcestructure (i.e., 2310 a) and a second source structure (i.e., 2310 b). Asecond distance is between the second source structure and a firstdetector structure (i.e., 2315 b). A third distance is between the firstdetector structure and a second detector structure (i.e., 2315 b).

In a first geometric arrangement shown in FIG. 12 , a first axis 2320passes through the reference point of the first and second sourcestructures and second detector structure. A second axis 2325 passesthrough the reference point of the first detector structure. The firstaxis is parallel to the second axis, but offset to the left of thesecond axis, i.e., the first and second axes are not coincident. In thisfirst geometric arrangement, the third distance is equal to the seconddistance. The first distance is less than the third or second distance.

However, many other different geometric arrangements are possible. Forexample, in a second geometric arrangement, a first axis passes throughthe reference point of the first and second source structures and firstdetector structure. A second axis passes through the reference point ofthe second detector structure. The first axis is parallel to the secondaxis, but offset to the left side of the second axis, i.e., the firstand second axes are not coincident. In this second geometricarrangement, the first and second distances are equal. The thirddistance is greater than the first or second distances.

In a third geometric arrangement, a first axis passes through thereference point of the second source structure and first and seconddetector structures. A second axis passes through the reference point ofthe first source structure. The first axis is parallel to the secondaxis, but offset to the left side of the second axis, i.e., the firstand second axes are not coincident. In this third geometric arrangement,the first distance is greater than the second distance, third distance,or both. The second distance is equal to the third distance.

In a fourth geometric arrangement, a first axis passes through thereference point of the first and second detector structures and thefirst source structure. A second axis passes through the reference pointof the second source structure. The first axis is parallel to the secondaxis, but offset to the left side of the second axis, i.e., the firstand second axes are not coincident. In this fourth geometricarrangement, the third distance is less than the first distance, seconddistance, or both. The first distance is equal to the second distance.

In a fifth geometric arrangement, a first axis passes through thereference point of the first and second source structures. A second axispasses through the reference point of the first and second detectorstructures. The first axis is parallel to the second axis, but offset tothe left side of the second axis, i.e., the first and second axes arenot coincident. In this fifth geometric arrangement, the second distanceis greater than the first distance, the third distance, or both. Thefirst distance equals the third distance.

In a sixth geometric arrangement, a first axis passes through thereference point of the first and second detector structures. A secondaxis passes through the reference point of the first and second sourcestructures. The first axis is parallel to the second axis, but offset tothe left side of the second axis, i.e., the first and second axes arenot coincident. In this sixth geometric arrangement, the second distanceis greater than the first distance, the third distance, or both. Thefirst distance equals the third distance.

In a seventh geometric arrangement, a first axis passes through thereference point of the second source structure and second detectorstructure. A second axis passes through the reference point of the firstsource structure and first detector structure. The first axis isparallel to the second axis, but offset to the left side of the secondaxis, i.e., the first and second axes are not coincident. In thisseventh geometric arrangement, the first, second, and third distancesare equal.

In an eighth geometric arrangement, a first axis passes through thereference point of the first source structure and first detectorstructure. A second axis passes through the reference point of thesecond source structure and second detector structure. The first axis isparallel to the second axis, but offset to the left side of the secondaxis, i.e., the first and second axes are not coincident. In this eighthgeometric arrangement, the first, second, and third distances are equal.

In a ninth geometric arrangement, a first axis passes through thereference point of the first source structure and second detectorstructure. A second axis passes through the reference point of thesecond source structure and first detector structure. The first axis isparallel to the second axis, but offset to the left side of the secondaxis, i.e., the first and second axes are not coincident. In this ninthgeometric arrangement, the second distance is less than the firstdistance, third distance, or both. The first distance is equal to thethird distance.

In a tenth geometric arrangement, a first axis passes through thereference point of the second source structure and first detectorstructure. A second axis passes through the reference point of the firstsource structure and second detector structure. The first axis isparallel to the second axis, but offset to the left side of the secondaxis, i.e., the first and second axes are not coincident. In this tenthgeometric arrangement, the second distance is less than the firstdistance, third distance, or both. The first distance is equal to thethird distance.

FIG. 12 shows various source and detector geometric arrangements withrespect to the tip having four openings. However, similar geometricarrangements may be had for tips with more than four or less than fouropenings. FIG. 13 shows a source and detector geometric arrangementwhere the tip includes three openings. This specific example includes asource structure 2410 and detector structures 2415 a and 2415 b. A firstdistance is between the source structure and a first detector structure(i.e., 2415 a). A second distance is between the first detectorstructure and a second detector structure (i.e., 2415 b). The source anddetector structures may be arranged on a line. In this first geometricarrangement, the first and second distances are equal.

However, many other different geometric arrangements are possible. Forexample, in a second geometric arrangement, the first distance is lessthan the second distance.

In a third geometric arrangement, the first distance is greater than thesecond distance.

FIG. 13 shows various geometric arrangements of source and detectorstructures relative to a single axis where the source and detectorstructures are arranged on the same line. However, other geometricarrangements may instead or additionally have distances between sourceand detector arrangements relative to a second axis.

For example, FIG. 14 shows another example of a geometric arrangementhaving distances relative to an x-axis. This specific example includesthree sensors including a source structure 2510 and detector structures2515 a and 2515 b. A first distance is between the source structure anda first detector structure (i.e., 2515 a). A second distance is betweenthe first detector structure and a second detector structure (i.e., 2515b).

In a first geometric arrangement shown in FIG. 14 , a first axis 2520passes through the reference point of source structure and firstdetector structure. A second axis 2525 passes through the referencepoint of the second detector structure. The first axis is parallel tothe second axis, but offset to the left side of the second axis, i.e.,the first and second axes are not coincident. In this first geometricarrangement, the first distance is less than the second distance.

However, many other different geometric arrangements are possible. Forexample, in a second geometric arrangement, a first axis passes throughthe reference point of the first and second detector structures. Asecond axis passes through the reference point of the source structure.The first axis is parallel to the second axis, but offset to the leftside of the second axis, i.e., the first and second axes are notcoincident. In this second geometric arrangement, the first distance isgreater than the second distance.

In a third geometric arrangement, a first axis passes through thereference point of the first source structure and second detectorstructure. A second axis passes through the reference point of the firstdetector structure. The first axis is parallel to the second axis, butoffset to the left side of the second axis, i.e., the first and secondaxes are not coincident. In this third geometric arrangement, the firstdistance is equal to the second distance.

In a fourth geometric arrangement, a first axis passes through thereference point of the first detector structure. A second axis passesthrough the reference point of the first source structure and seconddetector structure. The first axis is parallel to the second axis, butoffset to the left side of the second axis, i.e., the first and secondaxes are not coincident. In this fourth geometric arrangement, the firstdistance is equal to the second distance.

FIG. 14 shows various source-detector geometric arrangements withrespect to the tip having three openings. However, similar geometricarrangements may be had for tips with less than three openings, such astwo openings.

FIG. 15 shows a source and detector geometric arrangement where the tipincludes two openings. This specific example includes a source structure2610 and a detector structure 2615. A first axis 2620 passes through thereference point of the source structure. A second axis 2625 passesthrough the reference point of the detector structure. The first axis isparallel to the second axis, but offset to the left side of the secondaxis, i.e., the first and second axes are not coincident.

In another embodiment, a first axis passes instead through the referencepoint of the detector structure and the second axis passes through thereference point of the source structure. The first axis is parallel tothe second axis, but offset to the left side of the second axis, i.e.,the first and second axes are not coincident.

FIGS. 16 through 19C show additional patterns of source structures anddetector structures in an oximeter sensor in asymmetric arrangements.Each figure shows a particular opening pattern, and any of these may beused in conjunction with any of the implementations discussed in thisapplication. Contrary to FIGS. 7-15 which illustrate the entire bottomsurface of a retractor tip including a retractor portion, FIGS. 16through 19C illustrate just sensor openings. A retractor portion orblade can be located at any suitable position in embodiments shown inFIGS. 16 through 19C.

FIG. 16 shows a specific implementation of an oximeter sensor. Thissensor has six openings 1601-1606. Openings 1601-1604 are arranged in aline closer to a first edge of the sensor, while openings 1605 and 1606are arranged closer to a second edge, which is opposite the first edge.In fact, opening 1606 is closer than opening 1605 to the second edge.These openings are for sources and detectors, and there can be anynumber of sources, any number of detectors, and they can be in anycombination. In an implementation of an oximeter sensor, the first edgeis distal to the second edge, which is closer to a cable attached to theprobe or hand holding the probe.

In one implementation, openings 1601-1604 are detectors while openings1605 and 1606 are sources. However, in other implementations, there canbe one or more detectors, two or more detectors, one or more sources, ortwo or more sources. For example, there may be three detectors and threesources or one detector and five sources.

In FIG. 16 , the openings are positioned asymmetrically such that a linedrawn through openings 1601-1604 is not parallel to a line drawn throughopenings 1605 and 1606. However, a line drawn through openings 1601 and1605 is parallel to a line through openings 1604 and 1606. Additionally,the distance between openings 1601 and 1604 is shorter than the distancebetween openings 1605 and 1606.

Thus, the distance between openings 1601 and 1605 does not equal thedistance between openings 1601 and 1606; the distance between openings1602 and 1605 does not equal the distance between openings 1603 and1605; and the distance between openings 1603 and 1605 does not equal thedistance between openings 1604 and 1606.

In this implementation, the oximeter sensor has a rectangular shape, butthe sensor unit may have any shape such a trapezoid, triangle,dodecagon, octagon, hexagon, square, circle, or ellipse. A sensor of anyshape or form can incorporate the sensor openings in the pattern shownand described.

In a specific implementation, a distance between openings 1601 and 1604is five millimeters. A distance between each of the openings 1601, 1602,1603, and 1604 is 5/3 millimeters. A distance between 1601 and 1605 isfive millimeters. A diameter of an opening is one millimeter.

FIG. 17 shows a variation of the implementation of the oximeter sensorshown in FIG. 16 . The oximeter sensor in this specific implementationis also arranged to include six openings 1701-1706. Similar to FIG. 16 ,openings 1701-1704 are arranged in a line closer to a first edge of thesensor, while openings 1705 and 1706 are arranged closer to a secondedge, which is opposite the first edge. In one implementation, openings1701-1704 are detectors while openings 1705 and 1706 are sources.

In this figure, the openings are positioned so that a line drawn throughopenings 1701-1704 is parallel to a line through openings 1705 and 1706.However, a line drawn through openings 1701 and 1705 is not parallel toa line through openings 1704 and 1706.

Additionally, similar to FIG. 16 , the distance between openings 1701and 1704 is shorter than the distance between openings 1705 and 1706.Thus, the distance between openings 1701 and 1705 does not equal thedistance between openings 1701 and 1706; the distance between openings1702 and 1705 does not equal the distance between openings 1703 and1705; and the distance between openings 1703 and 1705 does not equal thedistance between openings 1704 and 1706.

In this implementation, the oximeter sensor unit itself is of a greaterarea relative to the area of the oximeter sensor unit shown in FIG. 16 .In another implementation, the oximeter sensor unit may be of a smallerarea relative to the area shown in FIG. 16 . In yet anotherimplementation, the oximeter sensor unit may be of a greater arearelative to that shown in FIG. 16 .

Further, in a specific implementation, the openings are the same size aseach other (e.g., each opening has the same diameter or each opening hasthe same area). A specific implementation uses one-millimeter circularopenings. However, in another implementation, the diameter of oneopening may be different from other openings, or there may be someopenings with different diameters than other openings. There can be anycombination of differently sized openings on one sensor unit. Forexample, there are two openings with a C size and other openings have aD size, where C and D are different and D is greater than C. Also,openings are not necessarily circular. So, C and D may represent areavalues.

FIG. 18 shows a specific implementation of an oximeter sensor which isarranged to include four openings 1801-1804. Openings 1801 and 1802 arearranged in a line closer to a first edge of the sensor, while openings1803 and 1804 are arranged closer to a second edge, which is oppositethe first edge. In fact, opening 1804 is closer than opening 1803 to thesecond edge. In an implementation the first edge is distal to the secondedge, which is closer to a cable attached to the probe or hand holdingthe probe.

In one implementation, openings 1801 and 1802 are detector structuresand openings 1803 and 1804 are source structures. However, in otherimplementations, there can be one or more detector structures, two ormore detector structures, one or more source structures, or two or moresource structures. For example, there may be three detector structuresand one source structure or one detector structure and three sourcestructures.

In FIG. 18 , the openings are positioned asymmetrically such that a linedrawn through openings 1801 and 1802 is not parallel to a line throughopenings 1803 and 1804. However, a line drawn through openings 1801 and1803 is parallel to a line through openings 1802 and 1804.

Additionally, the distance between openings 1801 and 1802 is shorterthan the distance between openings 1803 and 1804. Thus, in FIG. 18 , thedistance between openings 1801 and 1803 does not equal the distancebetween openings 1802 and 1804 and the distance between openings 1802and 1803 does not equal that between openings 1802 and 1804.

FIG. 19A shows another variation of the implementation of the oximetersensor. This implementation of an oximeter sensor is similarly arrangedto include four openings 1901-1904. Also, this arrangement of openingsis located closer to a first edge of the sensor. However, in thisfigure, openings 1901, 1902, and 1904 lie in a row parallel to the firstedge so that a straight line may be drawn through the center of eachopening, while opening 1903 lies below that straight line.

In this implementation, opening 1903 lies equally spaced betweenopenings 1902 and 1904; in other implementations, opening 1903 can liecloser to one opening than another. In one implementation, openings 1901and 1902 are detectors and openings 1903 and 1904 are sources.

In this specific implementation, as mentioned above, the distancebetween openings 1902 and 1903 equals that between openings 1903 and1904. Aside from this equality, the distances between the openings areunequal. For example, in this implementation, the distance betweenopenings 1901 and 1903 does not equal the distance between openings 1902and 1904 and the distance between openings 1902 and 1903 does not equalthat between openings 1902 and 1904.

Although oximeter sensors with two, four, and six openings are shown inthese figures, other implementations may include different numbers ofsensor openings. For instance, there may be three, five, seven, eight,or more openings.

Further, there may be any combination of detector structures and sourcestructures and the number of detector structures need not equal thenumber of source structures. For instance, if there are three openings,there may be one detector structure and two source structures or twodetector structures and one source structure. As another example, ifthere are eight openings, there may be two detector structures and sixsource structures, five detector structures and three source structures,or four detector structures and four source structures.

In another implementation of the invention, an oximeter sensor at thetip of a retractor includes only a single opening, rather than multipleopenings, and a single optical fiber or single optical fiber bundle isconnected to the single opening. The optical fiber or optical fiberbundle may be made of glass or plastic. In this implementation, a singleoptical fiber or fiber bundle is used to emit light into a tissue and toreceive reflected light from the tissue from the same opening at theretractor tip.

FIGS. 19B-1 and 19B-2 illustrate an implementation where a single glassoptical fiber bundle is connected to a single opening at the tip of aretractor. Shown in FIG. 19B-2 is a single optical fiber bundle 1911which is connected to a single opening in the tip of a retractor(referred to as “probe head” 1913 in FIG. 19B-2 ). A cross section of afiber bundle 1911 c shows that about a half of the optical fibers in thebundle (referred to as optical fibers 1922) is used for emitting light.The other half of the optical fibers in the bundle (referred to asoptical fibers 1924) is used for returning light.

As shown in FIGS. 19B-1 and 19B-2 , optical fibers 1922 are connected toa laser diode 1917, and optical fibers 1924 are connected to aphotodiode 1920. When light is emitted from laser diode 1917, opticalfibers 1922 carry the light into the tissue. The light scatters in thetissue and is reflected back to optical fibers 1924 which return anattenuated version of the light to the photodiode. The emitting lightand returning light travels in the same single fiber bundle, but inopposite direction.

Any suitable number of optical fibers can be contained in a singlebundle. For example, an optical fiber bundle may contain two (a firstfiber for emitting light and a second fiber for returning light), three,four, five, six, tens, hundreds, or more optical fibers. In an opticalfiber bundle, a number of optical fibers used for emitting light may notequal to those used for returning light. For example, if the bundle hasfive optical fibers, two optical fibers may be used for emitting lightand three optical fibers may be used for returning light, or vice versa.

FIGS. 19C-1, 19C-2, and 19C-3 illustrate another implementation of theinvention where a distal end of a single plastic optical fiber 1931 (nota bundle) is connected to an opening at the tip of a retractor (referredto as “probe head” 1933). At a proximal end of single optical fiber1931, the fiber is connected to two separate optical fibers 1935 and1937 by a 1-to-2 (i.e., Y-shaped) fiber combiner 1939. Typically, thefiber combiner contains a black separating bar 1941 to reduce cross talkbetween the emitting light and returning light at the two surfacesbetween the three fibers.

In the implementations shown in FIGS. 19B-1, 19B-2, 19C-1, 19C-2, and19C-3 , the returning light is mainly light back scattered by hemoglobinin the skin and a shallow volume of tissue underneath the skin. This isbecause a distance between an emitting optical fiber and returningoptical fiber is less than the diameter of the optical fiber bundle(e.g., 1 millimeter). The light being returned has not traveled deeplyinto the tissue. Therefore, the returning light carries more informationabout oxygen saturation level of the skin and a shallow volume of tissueunderneath the skin, not a whole block of tissue deep underneath theskin. Accordingly, the implementations shown in FIGS. 19B-1, 19B-2,19C-1, 19C-2, and 19C-3 are particularly useful in measuring oxygensaturation of a thin layer of tissue.

FIG. 20 shows a system 2001 for retracting a tissue and for measuringone or more parameters associated with a retracted tissue. The system2001 contains a system unit 2005 and a sensor probe 2008 (which is aretractor having one or more sensors), which is connected to the systemunit via a wired connection 2012. In one implementation, the system unit2005 may be a controller described above and shown in FIG. 1 . Inanother embodiment, the system unit 2005 may be a system unit describedabove and shown in FIG. 5A.

In FIG. 20 , connection 2012 may be an electrical, optical, or anotherwired connection including any number of wires (e.g., one, two, three,four, five, six, or more wires or optical fibers), or any combination ofthese or other types of connections. In other implementations of theinvention, however, connection 2012 may be wireless such as via a radiofrequency (RF) or infrared communication.

Typically, the system is used by placing the sensor probe in contact orclose proximity to tissue (e.g., skin) at a site where an oxygensaturation, force, or other related measurement is desired. The systemunit causes an input signal to be emitted by source structures in thesensor probe into the tissue (e.g., human tissue). There may be multipleinput signals, and these signals may have varying or differentwavelengths. The input signal is transmitted into or through the tissue.

Then, after transmission through or reflection off the tissue, thesignal is received by detector structures in the sensor probe. Thisreceived signal is received and analyzed by the system unit. Based onthe received signal, the system unit determines the oxygen saturation orother parameters of the tissue and provides an output signal (e.g., avisual or audible signal).

In an implementation, the system is a tissue oximeter, which can measureoxygen saturation without requiring a pulse or heart beat. A tissueoximeter of the invention is applicable to many areas of medicine andsurgery including plastic surgery. The tissue oximeter can make oxygensaturation measurements of tissue where there is no pulse; such tissue,for example, may have been separated from the body (e.g., a flap) andwill be transplanted to another place in the body.

Aspects of the invention are also applicable to a pulse oximeter. Incontrast to a tissue oximeter, a pulse oximeter requires a pulse inorder to function. A pulse oximeter typically measures the absorbance oflight due to the pulsing arterial blood.

There are various implementations of systems and techniques formeasuring oxygen saturation such as discussed in U.S. Pat. Nos.6,516,209, 6,587,703, 6,597,931, 6,735,458, 6,801,648, and 7,247,142.These patents are assigned to the same assignee as this patentapplication and are incorporated by reference.

Various equations for self-calibration schemes are also known in theart. Self-calibration schemes are used to adjust for system factors suchas source intensity, detector gain, and loss of light in the opticalfibers and connectors. The self-calibration scheme may include equationsdiscussed in U.S. Pat. Nos. 6,516,209, 6,735,458, and 6,078,833, and NewOptical Probe Designs for Absolute (Self-Calibrating) NIR TissueHemoglobin Measurements, Proc. SPIE 3597, pages 618-631 (1999), whichare incorporated by reference.

The attenuation ratio method may also include techniques discussed inU.S. Pat. No. 6,587,701, which is incorporated by reference. Theattenuation ratio method is used to determine tissue oxygenation,hemoglobin concentration, or both. Additional detail on self-calibrationschemes and attenuation ratio methods is also discussed in U.S. patentapplication Ser. No. 12/126,860, filed May 24, 2008, which isincorporated by reference.

FIG. 21 shows a specific implementation of the system of FIG. 20 , wheresome of the components of the system are shown in greater detail. Thesystem unit includes a processor 2104, display 2107, speaker 2109,signal emitter 2131, signal detector 2133, volatile memory 2112,nonvolatile memory 2115, human interface device or HID 2119, I/Ointerface 2122 (e.g., USB), and network interface 2126. These componentscan be housed within a single system unit enclosure or separately.Different implementation of the system may include any number of thecomponents described, in any combination or configuration, and may alsoinclude other components not shown.

The components are linked together using a bus 2103, which representsthe system bus architecture of the system. Although this figure showsone bus that connects to each component, the busing is illustrative ofany interconnection scheme serving to link the subsystems. For example,speaker 2109 could be connected to the other subsystems through a portor have an internal direct connection to processor 2104.

A sensor probe 2146 of the system includes a probe 2138 and connector2136. The probe is connected to the connector using one or more wires2142 and 2144. The connector removably connects the probe and its wiresto the signal emitter and signal detectors in the system unit. There isone cable or set of cables 2142 to connect to the signal emitter, andone cable or set of cables 2144 to connect to the signal detector. In animplementation the cables are fiber optic cables, but in otherimplementations, the cables are electrical wires.

Signal emitter 2131 is a light source that emits light at one or morespecific wavelengths. In a specific implementation, two wavelengths oflight (e.g., 690 nanometers and 830 nanometers) are used. In otherimplementations, other wavelengths of light may be used. The signalemitter is typically implemented using a laser diode or light emittingdiode (LED). Signal detector 2133 is typically a photodetector capableof detecting the light at the wavelengths produced by the signalemitter.

The connector may have a locking feature; e.g., insert connector, andthen twist or screw to lock. If so, the connector is more securely heldto the system unit and it will need to be unlocked before it can beremoved. This will help prevent accidental removal of the probe.

The connector may also have a first keying feature, so that theconnector can only be inserted into a connector receptacle of the systemunit in one or more specific orientations. This will ensure that properconnections are made.

The connector may also have a second keying feature that provides anindication to the system unit which type of probe is attached. Thesystem unit may handle making measurements for a number of differenttypes of probes. When a probe is inserted, the system uses the secondkeying feature to determine which type of probe is connected to thesystem. Then the system can perform the appropriate functions, use theproper algorithms, or otherwise make adjustments in its operation forthe specific probe type.

For example, when the system detects that a cerebral probe is connected,the system uses cerebral probe algorithms and operation. When the systemdetects a nerve retractor probe is connected, the system uses nerveretractor probe algorithms and operation. A system can handle any numberof different types of probes. There may be different probes formeasuring different parts of the body, or different sizes or versions ofprobe for measuring a part of the body (e.g., three different nerveretractor probe models).

With the second keying feature, the system will be able to distinguishbetween the different probes. The second keying feature can use any typeof coding system to represent each probe including binary coding. Forexample, for a probe, there are four second keying inputs, each of whichcan be a logic 0 or 1. With four second keying inputs, the system willbe able to distinguish between sixteen different probes.

In some applications, probe 2146 can be a handheld tool and a user movesthe probe from one point to another to make measurements. In otherapplications, probe 2146 can be part of an endoscopic instrument orrobotic instrument, or both. For example, the probe is moved or operatedusing a guiding interface, which may or may not include haptictechnology.

In various implementations, the system is powered using a wall outlet orbattery powered, or both. Block 2151 shows a power block of the systemhaving both AC and battery power options. In an implementation, thesystem includes an AC-to-DC converter 2153. The converter takes AC powerfrom a wall socket, converts AC power to DC power, and the DC output isconnected to the components of the system needing power (indicated by anarrow 2154). In an implementation, the system is battery operated. TheDC output of a battery 2156 is connected to the components of the systemneeding power (indicated by an arrow 2157). The battery is rechargedusing a recharger circuit 2159, which received DC power from an AC-DCconverter. The AC-to-DC converter and recharger circuit may be combinedinto a single circuit.

The nonvolatile memory may include mass disk drives, floppy disks,magnetic disks, optical disks, magneto-optical disks, fixed disks, harddisks, CD-ROMs, recordable CDs, DVDs, recordable DVDs (e.g., DVD-R,DVD+R, DVD-RW, DVD+RW, HD-DVD, or Blu-ray Disc), flash and othernonvolatile solid-state storage (e.g., USB flash drive),battery-backed-up volatile memory, tape storage, reader, and othersimilar media, and combinations of these.

The processor may include multiple processors or a multicore processor,which may permit parallel processing of information. Further, the systemmay also be part of a distributed environment. In a distributedenvironment, individual systems are connected to a network and areavailable to lend resources to another system in the network as needed.For example, a single system unit may be used to collect results fromnumerous sensor probes at different locations.

Aspects of the invention may include software executable code orfirmware (e.g., code stored in a read only memory or ROM chip). Thesoftware executable code or firmware may embody algorithms used inmaking oxygen saturation measurements of the tissue. The softwareexecutable code or firmware may include code to implement a userinterface by which a user uses the system, displays results on thedisplay, and selects or specifies parameters that affect the operationof the system.

Further, a computer-implemented or computer-executable version of theinvention may be embodied using, stored on, or associated with acomputer-readable medium. A computer-readable medium may include anymedium that participates in providing instructions to one or moreprocessors for execution. Such a medium may take many forms including,but not limited to, nonvolatile, volatile, and transmission media.Nonvolatile media includes, for example, flash memory, or optical ormagnetic disks. Volatile media includes static or dynamic memory, suchas cache memory or RAM. Transmission media includes coaxial cables,copper wire, fiber optic lines, and wires arranged in a bus.Transmission media can also take the form of electromagnetic, radiofrequency, acoustic, or light waves, such as those generated duringradio wave and infrared data communications.

For example, a binary, machine-executable version, of the software ofthe present invention may be stored or reside in RAM or cache memory, oron a mass storage device. Source code of the software of the presentinvention may also be stored or reside on a mass storage device (e.g.,hard disk, magnetic disk, tape, or CD-ROM). As a further example, codeof the invention may be transmitted via wires, radio waves, or through anetwork such as the Internet. Firmware may be stored in a ROM of thesystem.

Computer software products may be written in any of various suitableprogramming languages, such as C, C++, C#, Pascal, Fortran, Perl, Matlab(from MathWorks, www.mathworks.com), SAS, SPSS, JavaScript, AJAX, andJava. The computer software product may be an independent applicationwith data input and data display modules. Alternatively, the computersoftware products may be classes that may be instantiated as distributedobjects. The computer software products may also be component softwaresuch as Java Beans (from Sun Microsystems) or Enterprise Java Beans (EJBfrom Sun Microsystems).

An operating system for the system may be one of the Microsoft Windows®family of operating systems (e.g., Windows 95, 98, Me, Windows NT,Windows 2000, Windows XP, Windows XP x64 Edition, Windows Vista, Windows7, Windows CE, Windows Mobile), Linux, HP-UX, UNIX, Sun OS, Solaris, MacOS X, Alpha OS, AIX, IRIX32, or IRIX64. Microsoft Windows is a trademarkof Microsoft Corporation. Other operating systems may be used, includingcustom and proprietary operating systems.

Furthermore, the system may be connected to a network and may interfaceto other systems using this network. The network may be an intranet,internet, or the Internet, among others. The network may be a wirednetwork (e.g., using copper), telephone network, packet network, anoptical network (e.g., using optical fiber), or a wireless network, orany combination of these. For example, data and other information may bepassed between the computer and components (or steps) of a system of theinvention using a wireless network using a protocol such as Wi-Fi (IEEEstandards 802.11, 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, and802.11n, just to name a few examples). For example, signals from asystem may be transferred, at least in part, wirelessly to components orother systems or computers.

In an embodiment, through a Web browser or other interface executing ona computer workstation system or other device (e.g., laptop computer,smartphone, or personal digital assistant), a user accesses a system ofthe invention through a network such as the Internet. The user will beable to see the data being gathered by the machine. Access may bethrough the World Wide Web (WWW). The Web browser is used to downloadWeb pages or other content in various formats including HTML, XML, text,PDF, and postscript, and may be used to upload information to otherparts of the system. The Web browser may use uniform resourceidentifiers (URLs) to identify resources on the Web and hypertexttransfer protocol (HTTP) in transferring files on the Web.

This description of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form described, and manymodifications and variations are possible in light of the teachingabove. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications.This description will enable others skilled in the art to best utilizeand practice the invention in various embodiments and with variousmodifications as are suited to a particular use. The scope of theinvention is defined by the following claims.

The invention claimed is:
 1. A system comprising: a retractor, for retracting a tissue, comprising a shaft, a handle coupled to a proximal end of the shaft, a tip coupled to a distal end of the shaft, wherein the tip comprises a retractor portion and an oximeter sensor; a force sensor coupled to the retractor, wherein the force sensor comprises a load cell having a first end and a second end on opposite sides of each other, along an axis of the load cell; one or more optical fibers, wherein the one or more optical fibers pass through a channel in the shaft and distal ends of the one or more optical fibers are coupled to one or more openings of the tip; and a signal emitter circuit and a signal detector circuit, coupled to the one or more optical fibers, wherein the signal emitter circuit sends a signal through from the one or more optical fibers, and the signal detector circuit receives a signal through the one or more optical fibers; a processor, coupled to the signal emitter circuit and signal detector circuit, wherein the processor processes signals received through the one or more optical fibers; a display, coupled to the processor, wherein the display shows results of the processing by the processor, wherein the force sensor is located between the handle and the tip of the retractor, the force sensor measures force in a first direction, the handle extends in the first direction, and the tip of the retractor extends in a second direction, angled in a range from about 90 degrees to about 45 degrees to the first direction.
 2. The system of claim 1 wherein the force sensor is electrically coupled to the display, and the display can show an amount of force being measured by the force sensor.
 3. The system of claim 1 wherein the display is a first display, the force sensor is electrically coupled to a second display, and the second display can show an amount of force being measured by the force sensor.
 4. The system of claim 1 wherein load cell comprises an electronic load cell.
 5. The system of claim 1 wherein the tip of the retractor comprises a blade extending in a direction away from a surface of the tip, and there are at least two adjacent openings on the retractor tip that are positioned on the surface of the tip on one side of the blade.
 6. The system of claim 1 wherein the force sensor measures a component of force in a first direction, and at least one optical fiber is coupled to one opening of the tip to transmit light in the first direction.
 7. The system of claim 1 wherein the one or more optical fibers comprise a first optical fiber and a second optical fiber and the one or more openings of the tip comprise a first sensor opening and a second sensor opening, wherein a distal end of the first optical fiber is coupled to the first sensor opening of the tip, and a distal end of the second optical fiber is coupled to the second sensor opening of the tip, and wherein the signal emitter circuit sends a signal through the first optical fiber and the signal detector circuit receives the signal from the second optical fiber.
 8. The system of claim 7 wherein the oximeter sensor comprises the first sensor opening and second sensor opening on a bottom side of the tip, and the first sensor opening and second sensor opening are separated by about five millimeters or less.
 9. The system of claim 1 wherein the oximeter sensor comprises a first sensor emitter opening, a second sensor emitter opening, a first sensor detector opening, and a second sensor detector opening, wherein at least three of the four openings are positioned in a linear arrangement on a bottom side of the tip.
 10. The system of claim 1 wherein the signal emitter circuit causes an optical signal, having a wavelength from about 600 nanometers to about 900 nanometers, to be transmitted through a first sensor opening.
 11. The system of claim 1 wherein the signal emitter circuit causes an optical signal having two or more different wavelengths to be transmitted through a first sensor opening.
 12. The system of claim 11 wherein a first wavelength of the two or more different wavelengths is about 690 nanometers, and a second wavelength of the two or more different wavelengths is about 830 nanometers.
 13. The system of claim 1 wherein the retractor is a nerve retractor and the tissue is a nerve.
 14. The system of claim 1 wherein the retractor is a heart retractor and the tissue is a heart.
 15. The system of claim 1 wherein the tissue is at least one of a liver, kidney, lung, brain, muscle, stomach, intestine, uterus, ovary, bladder, bone, prostate, thyroid, parathyroid, adrenal gland, pancreas, or spleen.
 16. The system of claim 1 comprising: a positioning mechanism coupled to the retractor; and a controller coupled to the oximeter sensor and the positioning mechanism.
 17. The system of claim 1 comprising: a positioning mechanism physically coupled to the handle of the retractor and electrically coupled to a system unit.
 18. The system of claim 1 comprising a data recorder, wherein the force sensor is electrically coupled to the data recorder, and the data recorder stores force measurements.
 19. A system comprising: a retractor, for retracting a tissue, comprising a shaft, a handle coupled to a proximal end of the shaft, a tip coupled to a distal end of the shaft, wherein the tip comprises a retractor portion and an oximeter sensor; a force sensor coupled to the retractor, wherein the force sensor comprises a load cell having a first end and a second end on opposite sides of each other, along an axis of the load cell; one or more optical fibers, wherein the one or more optical fibers pass through a channel in the shaft and distal ends of the one or more optical fibers are coupled to one or more openings of the tip; and a signal emitter circuit and a signal detector circuit, coupled to the one or more optical fibers, wherein the signal emitter circuit sends a signal through from the one or more optical fibers, and the signal detector circuit receives a signal through the one or more optical fibers; a processor, coupled to the signal emitter circuit and signal detector circuit, wherein the processor processes signals received through the one or more optical fibers; a display, coupled to the processor, wherein the display shows results of the processing by the processor, wherein the handle of the retractor is a first handle and the system further comprises a second handle, and wherein the first end of the load cell is coupled to the first handle and the second end of the load cell is coupled to the second handle.
 20. The system of claim 19 wherein the force sensor is located between the handle and the tip of the retractor, the force sensor measures force in a first direction, the handle extends in the first direction, and the tip of the retractor extends in a second direction, angled in a range from about 90 degrees to about 45 degrees to the first direction.
 21. The system of claim 19 wherein the force sensor is electrically coupled to the display, and the display can show an amount of force being measured by the force sensor.
 22. The system of claim 19 wherein the display is a first display, the force sensor is electrically coupled to a second display, and the second display can show an amount of force being measured by the force sensor.
 23. The system of claim 19 wherein the load cell comprises an electronic load cell.
 24. The system of claim 19 wherein the tip of the retractor comprises a blade extending in a direction away from a surface of the tip, and there are at least two adjacent openings on the retractor tip that are positioned on the surface of the tip on one side of the blade.
 25. The system of claim 19 wherein the force sensor measures a component of force in a first direction, and at least one optical fiber is coupled to one opening of the tip to transmit light in the first direction.
 26. The system of claim 19 wherein the force sensor is located at the tip of the retractor.
 27. The system of claim 19 wherein the one or more optical fibers comprise a first optical fiber and a second optical fiber and the one or more openings of the tip comprise a first sensor opening and a second sensor opening, wherein a distal end of the first optical fiber is coupled to the first sensor opening of the tip, and a distal end of the second optical fiber is coupled to the second sensor opening of the tip, and wherein the signal emitter circuit sends a signal through the first optical fiber and the signal detector circuit receives the signal from the second optical fiber.
 28. The system of claim 27 wherein the oximeter sensor comprises the first sensor opening and second sensor opening on a bottom side of the tip, and the first sensor opening and second sensor opening are separated by about five millimeters or less.
 29. The system of claim 19 wherein the oximeter sensor comprises a first sensor emitter opening, a second sensor emitter opening, a first sensor detector opening, and a second sensor detector opening, wherein at least three of the four openings are positioned in a linear arrangement on a bottom side of the tip.
 30. The system of claim 19 wherein the signal emitter circuit causes an optical signal, having a wavelength from about 600 nanometers to about 900 nanometers, to be transmitted through a first sensor opening.
 31. The system of claim 19 wherein the signal emitter circuit causes an optical signal having two or more different wavelengths to be transmitted through a first sensor opening.
 32. The system of claim 31 wherein a first wavelength of the two or more different wavelengths is about 690 nanometers, and a second wavelength of the two or more different wavelengths is about 830 nanometers.
 33. The system of claim 19 wherein the retractor is a nerve retractor and the tissue is a nerve.
 34. The system of claim 19 wherein the retractor is a heart retractor and the tissue is a heart.
 35. The system of claim 19 wherein the tissue is at least one of a liver, kidney, lung, brain, muscle, stomach, intestine, uterus, ovary, bladder, bone, prostate, thyroid, parathyroid, adrenal gland, pancreas, or spleen.
 36. The system of claim 19 comprising: a positioning mechanism coupled to the retractor; and a controller coupled to the oximeter sensor and the positioning mechanism.
 37. The system of claim 19 comprising: a positioning mechanism physically coupled to the handle of the retractor and electrically coupled to a system unit.
 38. A system comprising: a retractor, for retracting a tissue, comprising a shaft, a handle coupled to a proximal end of the shaft, a tip coupled to a distal end of the shaft, wherein the tip comprises a retractor portion and an oximeter sensor; a force sensor coupled to the retractor, wherein the force sensor comprises a load cell having a first end and a second end on opposite sides of each other, along an axis of the load cell; one or more optical fibers, wherein the one or more optical fibers pass through a channel in the shaft and distal ends of the one or more optical fibers are coupled to one or more openings of the tip; and a signal emitter circuit and a signal detector circuit, coupled to the one or more optical fibers, wherein the signal emitter circuit sends a signal through from the one or more optical fibers, and the signal detector circuit receives a signal through the one or more optical fibers; a processor, coupled to the signal emitter circuit and signal detector circuit, wherein the processor processes signals received through the one or more optical fibers; a display, coupled to the processor, wherein the display shows results of the processing by the processor, wherein the oximeter sensor comprises a first sensor emitter opening, a second sensor emitter opening, a first sensor detector opening, and a second sensor detector opening, wherein at least three of the four openings are positioned in a linear arrangement on a bottom side of the tip, and wherein the second sensor emitter opening is between the first sensor emitter opening and the first sensor detector opening, and the first sensor detector opening is between the second sensor emitter opening and the second sensor detector opening, and wherein the first sensor detector opening is spaced away from the second sensor detector by about 5/3 millimeters or less, and the first sensor detector openings is spaced away from the second sensor emitter opening by about 5/3 millimeters or less.
 39. The system of claim 38 wherein the force sensor is located between the handle and the tip of the retractor, the force sensor measures force in a first direction, the handle extends in the first direction, and the tip of the retractor extends in a second direction, angled in a range from about 90 degrees to about 45 degrees to the first direction.
 40. The system of claim 38 wherein the signal emitter circuit causes an optical signal, having a wavelength from about 600 nanometers to about 900 nanometers, to be transmitted through a first sensor opening.
 41. The system of claim 38 wherein the signal emitter circuit causes an optical signal having two or more different wavelengths to be transmitted through a first sensor opening.
 42. The system of claim 41 wherein a first wavelength of the two or more different wavelengths is about 690 nanometers, and a second wavelength of the two or more different wavelengths is about 830 nanometers.
 43. The system of claim 38 wherein the force sensor is electrically coupled to the display, and the display can show an amount of force being measured by the force sensor.
 44. The system of claim 38 wherein the display is a first display, the force sensor is electrically coupled to a second display, and the second display can show an amount of force being measured by the force sensor.
 45. The system of claim 38 wherein load cell comprises an electronic load cell.
 46. The system of claim 38 wherein the tip of the retractor comprises a blade extending in a direction away from a surface of the tip, and there are at least two adjacent openings on the retractor tip that are positioned on the surface of the tip on one side of the blade.
 47. The system of claim 38 wherein the force sensor measures a component of force in a first direction, and at least one optical fiber is coupled to one opening of the tip to transmit light in the first direction.
 48. The system of claim 38 wherein the force sensor is located at the tip of the retractor.
 49. The system of claim 38 wherein the one or more optical fibers comprise a first optical fiber and a second optical fiber and the one or more openings of the tip comprise a first sensor opening and a second sensor opening, wherein a distal end of the first optical fiber is coupled to the first sensor opening of the tip, and a distal end of the second optical fiber is coupled to the second sensor opening of the tip, and wherein the signal emitter circuit sends a signal through the first optical fiber and the signal detector circuit receives the signal from the second optical fiber.
 50. The system of claim 49 wherein the oximeter sensor comprises the first sensor opening and second sensor opening on a bottom side of the tip, and the first sensor opening and second sensor opening are separated by about five millimeters or less.
 51. The system of claim 38 wherein the retractor is a nerve retractor and the tissue is a nerve.
 52. The system of claim 38 wherein the retractor is a heart retractor and the tissue is a heart.
 53. The system of claim 38 wherein the tissue is at least one of a liver, kidney, lung, brain, muscle, stomach, intestine, uterus, ovary, bladder, bone, prostate, thyroid, parathyroid, adrenal gland, pancreas, or spleen.
 54. The system of claim 38 comprising: a positioning mechanism coupled to the retractor; and a controller coupled to the oximeter sensor and the positioning mechanism.
 55. The system of claim 38 comprising: a positioning mechanism physically coupled to the handle of the retractor and electrically coupled to a system unit. 